LIBRARY 

OF  THE 


UNIVERSITY  OF  CALIFORNIA. 


Class 


WORKS  OF 
PROF.  A.  PRESCOTT  FOLWELL 


PUBLISHED    BY 


JOHN  WILEY  &  SONS. 


Sewerage. 

The  Designing,  Construction,  and  Maintenance 
of  Sewerage  Systems.  8vo,  cloth,  $3.00. 

Water-supply  Engineering. 

The  Designing,  Construction,  and  Maintenance 
of  Water-supply  Systems,  both  City  and  Irriga- 
tion. 8vo,  cloth,  $4.00. 


SEWERAGE. 


THE   DESIGNING,    CONSTRUCTION,    AND 

MAINTENANCE 

OF 

SEWERAGE    SYSTEMS. 


BY 

A.    PRESCOTT    FOLWELL, 

Member  American  Society  of  Civil  Engineers; 
Past  President  American  Society  of  Municipal  Improvements; 
Editor  Municipal  Journal  and  Engineer. 


SIXTH    EDITION,   REVISED   AND   ENLARGED. 
TOTAL   ISSUE,   TWELVE   THOUSAND. 


OF  THE 

UNIVERSITY 

OF 


NEW  YORK: 
JOHN   WILEY   &   SONS. 

LONDON:   CHAPMAN  &   HALL,   LIMITED. 
1910 


Copyright,  1898,  1900,  1901.  1910, 

BY 
A.  PRESCOTT  FOLWELL. 


THE  SCIENTIFIC   PRESS 

ROBERT   DRUMMONO   AND    COMPANY 

BROOKLYN,    N.  Y. 


PREFACE  TO  THE  SIXTH  EDITION. 


DURING  the  eleven  years  since  the  first  edition  of  this  work 
appeared  there  have  been  few  modifications  of  the  ideas  involved 
in  sewer  design  and  construction,  the  most  important  being  due 
to  the  increasing  use  of  concrete.  Such  of  these  as  have  come 
to  the  author's  notice,  however,  he  has  endeavored  to  incorporate 
into  this  edition. 

In  the  matter  of  sewage  disposal  the  advance  in  knowledge 
and  in  practice  has  been  so  great  that,  after  considerably  increasing 
in  the  third  edition  the  space  devoted  to  this,  and  revising  the 
matter  in  the  following  editions,  the  author  finds  it  necessary  to 
practically  rewrite,  for  this  sixth  edition,  all  the  chapters  dealing 

with  that  subject. 

iii 


206169 


PREFACE  TO  THE  FIRST  EDITION. 


For  a  number  of  years  trie  author  has  been  looking  for  the 
appearance  of  a  work  on  Sewerage  which  should  embody  the 
most  recent  data  and  ideas  relating  to  the  subject  and  treat 
of  both  the  Combined  and  Separate  Systems  in  a  comprehen- 
sive manner,  recognizing  the  fact  that  such  a  work  is  needed 
by  city  engineers  and  engineering  schools.  None  such  has 
appeared,  and  he  has  consequently  undertaken  the  task  of 
supplying  the  deficiency. 

No  attempt  has  been  made  to  treat  at  length  the  subject 
of  Sewage  Disposal,  for  the  reasons  stated  in  Chapter  II. 
Parts  II  and  III  on  the  Construction  and  Maintenance  of 
Sewers  will,  he  believes,  be  appreciated  by  those  who  are 
called  upon  to  superintend  such  work  without  previous  experi- 
ence, and  even,  he  hopes,  give  valuable  hints  to  many  who 
are  not  novices;  although  he  recognizes  that  the  ground  is  by 
no  means  completely  covered.  For  much  of  the  matter 
therein  contained  he  is  indebted  to  the  engineering  peri- 
odicals, particularly  the  News  and  Record,  but  the  greater  part 
of  it  has  never,  to  his  knowledge,  appeared  in  print. 

While  primarily  intended  for  practising  engineers,  the 
work  has  also  been  arranged  with  the  idea  that  it  may  be 
useful  as  a  text-book  in  engineering  schools;  Part  I  having 
already  been  so  used  by  the  author,  and  Part  II  having  been 
largely  given  in  the  form  of  lectures  to  his  classes. 


CONTENTS. 


PART  I.     DESIGNING 

CHAPTER  I.    THE  SYSTEM. 

ART.  PAGE 

T-  Requirements  of  a  System I 

2.  Dry  Sewage  Methods 2 

3.  Dry  Sewage  Systems 4 

4.-  Pneumatic  Systems 7 

5.  Water-carriage  Systems 7 

6.  Combined  and  Separate  Systems 9 

7.  Summary  .  .  . "". 12 

CHAPTER  II.    AMOUNT  OF  SEWAGE. 

8.  Factors  in  the  Calculation 13 

9.  Amount  of  House-sewage 14 

10.  Data  of  House-sewage  Flow 21 

1 1 .  Amount  of  Storm-water 28 

12.  Rates  of  Rainfall 28 

13.  Run-off  Data 31 

14.  Formulas  for  Storm-water  Run-off 36 

15.  Expediency  of  Providing  for  Excessive  Storms 1 40 

CHAPTER  III.    FLOW  IN  SEWERS. 

16.  Fundamental  Theories : 44 

17.  Limits  of  Velocity 57 

18.  Size  of  Sewers 62 

19.  Shape  of  Sewers 65 

•    CHAPTER  IV.    FLUSHING  AND  VENTILATION. 

Necessity  for  Flushing .- 69 

21.  Methods  of  Flushing 72 

22.  Appliances  for  Flushing 77 

23.  Necessity  for  Ventilation 79 

24.  Methods  of  Ventilation 81 

v 


Vi  CONTENTS. 

CHAPTER  V.    COLLECTING  THE  DATA 
ART.  PAGB 

25.  Data  Required  87 

26.  Surveying  and  Plotting 90 

CHAPTER  VI.    THE  DESIGN. 

27.  General  Principles 95 

28.  Subdivision  into  Districts 100 

29.  Locating  the  Sewer  Lines 101 

30.  Volume  of  House-sewage 104 

31.  Volume  of  Storm-sewage 106 

32.  Grade,  Size  and  Depth  of  Sewers 115 

33.  Inverted  Siphons 122 

34.  Sub-drains 123 

35.  House  and  Inlet  Connections 125 

36.  Manholes,  Inlets,  Flush-tanks,  etc 128 

37.  Pumping  of  Sewage 132 

38.  Intercepting  Sewers  and  Overflows 137 

39.  Use  of  Old  Sewers 139 

CHAPTER  VII.    DETAIL  PLANS. 

o.  The  Sewer-barrel 141 

41.  Pipe  Sewers 151 

2.  Manholes,  Lamp-holes,  Flush-tanks,  etc 158 

43.  Interceptors  and  Overflows 170 

44.  Inverted  Siphons,  Sub-drains,  Foundations 172 

CHAPTER  VIII.    SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST. 

45.  Definition  and  Classification  of  Specifications 177 

46.  Specifications  for  Materials 179 

47.  "  "  Excavation 186 

48.  "  "  Construction 191 

49.  "  "  Back-filling  and  Cleaning  up 205 

50.  General  Provisions,  Payments,  etc 209 

51.  Contract 217 

52.  Estimate  of  Cost 220 

53.  Methods  of  Assessment 226 

PART  II.     CONSTRUCTION. 
CHAPTER  IX.    PREPARING  FOR  CONSTRUCTION. 

54.  Contract  Work  or  Day  Labor 233 

55.  Obtaining  Bids 235 


CONTENTS.  Vll 

ART.  PAGE 

56.  Engineering  Work  Preliminary  to  Construction 237 

57.  Other  Preliminaries  .  .  .. , 238 


CHAPTER  X.     LAYING  OUT  THE  WORK. 

58.  Lining  Out  Trenches 240 

59.  Giving  Grade 241 

CHAPTER  XL     OVERSIGHT  AND  MEASUREMENT  OF  WORK. 

60.  Inspection  of  Work 248 

61.  Duties  of  the  Engineer 250 

62.  Measurements 252 

63.  Final  Inspection 256 

CHAPTER  XII.    PRACTICAL  SEWER   CONSTRUCTION. 

64.  Organizing  the  Force 261 

65.  Trenching  by  Hand 266 

66.  Excavating  Machinery 271 

67.  Sheathing 275 

68.  Laying  Sewer  Pipe 287 

69.  Building  Masonry  Sewers 293 

70.  Building  Manholes  and  Other  Appurtenances 304 

71.  Foundations 307 

72.  Pumping  and  Draining 308 

73.  Handling  Wet  and  Quicksand  Trenches 313 

74.  River  Crossings  and  Outlets 326 

75.  Crossing  Railroads  and  Canals 333 


PART  III.    MAINTENANCE. 
CHAPTER  XIII.     HOUSE  CONNECTIONS  AND  DRAINAGE. 

.  Necessity  for  Intelligent  Maintenance 338 

.  Requirements  of  Sanitary  House-drainage 339 

CHAPTER  XIV.    SEWER  MAINTENANCE. 

78.  Requirements  of  Proper  Maintenance 345 

79.  Flushing 347 

80.  Cleaning 352 


viii  CONTENTS. 

PART  IV.     SEWAGE  DISPOSAL. 
CHAPTER  XV.    DISPOSAL  BY  DILUTION. 


ART. 


PAGE 


jgi.  "Disposal"  and  "Sewage"  Defined 359 

82.  Aims  of  Disposal 360 

83.  Principles  Involved 362 

Composition  of  Sewage 367 

Sewage  Analyses 375 

Pollution  of  Streams  and  Tidal  Waters . . .; 382 

87.  Aims  of  Treatment .  . 385 

88.  Disposal  by  Dilution 389 


CHAPTER  XVI.    METHODS  OF  TREATMENT. 

89.  General  Principles 397 

.90.  Straining 400 

Vi .  Tank  Treatment,  Sedimentation 403 

92.  Tank  Treatment,  Precipitation 410 

XJ3-  Tank  Treatment,  Septic  Tanks 419 

94.  Oxidation ' 429 

95.  Intermittent  Filtration  and  Irrigation 434 

96.  Contact  Filters,  Slate  Beds 448 

7.  Sprinkling  Filters , .  454 

Disinfection 467 

99.  Miscellaneous  Methods 474 

100.  Disposal  of  Sludge 478 

101.  Summary  . 484 


ILLUSTRATIONS. 

PLATE 

I.  Des  Moines  Sewer  Gaugings  and  Water  Consumption 25 

II.  New  Orleans  Run-off  Diagrams 33 

III.  Plan  of  a  House  Sewerage  System 107 

IV.  Rainfall  Diagrams  and  Acreage  Curve 109 

V.  Plan  of  a  Storm  Sewer  System 112 

VI.  Sections  of  Masonry  Sewers 144 

VII.         "       "          "           "    146 

VIII.  Sections  of  Masonry  and  Pipe  Sewers 148 

IX.  Manholes  and  Lamp-holes 159 

X.  Manholes,  Flush-tanks  and  Inlets 161 

XI.  Interceptors,  Siphons,  Sub-drains,  etc 171 

XII.  Normal  Chlorine  in  Massachusetts  and  Connecticut 371 


CONTENTS.  ix 

FIGURE  PAGE 

1.  Modified  Birmingham  Pail 5 

2.  Egg-shaped  Sewer 66 

3.  Sounding-rod 93 

30.  Sounding  Machine 93 

4.  Alignment  of  Sewer  Junctions 103 

5.  Joint  of  Reinforced  Concrete  Pipe 149 

6.  Method  of  Setting  Grade  Plank 242 

7.  "        "      "  "         "    243 

8.  Method  of  Holding  Grade  Cord 244 

9.  Grade  Rod 244 

10.  Inspector's  Templet  for  Egg-shaped  Sewer 258 

11.  Excavation  Platform 267 

12.  Cross-staging  in  Trench 268 

13.  Skeleton  Sheathing 277 

14.  Sheathing  under  Braces 279 

15.  Driving  Cap  and  Maul 280 

16.  Horizontal  Sheathing 281 

1 7.  Sliding  Rod  for  Measuring  Braces 282 

18.  Sheathing  Puller  .  . 285 

19.  Pipe-laying  Hook 288 

20.  Appliance  for  "Entering"  Heavy  Pipe 288 

21.  Pipe-cleaning  Disk 291 

22.  Templet  for  Brick  Sewers 294 

23.  Hod  for  Lowering  Brick 296 

24.  Masons'  Platform  for  Brick  Sewers 297 

25.  Center  for  Brick  Sewers 298 

26.  Form  for  Concrete  Arch 302 

27.  Sewer-pipe  Laid  in  Concrete 317 

28.  Sheathing  a  Badly  Caved  Trench 319 

29.  Appliance  for  Cleaning  Sub-drain 324 

30.  Sewer  Crossing  Creek  above  Water 327 

31.  Cofferdam  Puddle-walls 331 

32.  Sheathing  on  Steep  Slopes 335 

33.  Flange  for  Pipe  in  Embankment 336 

34.  Appliance  for  Cleaning  Siphon  Sump 353 

35.  Disk  for  Cleaning  Sewers 355 

36.  Method  of  Using  Cleaning  Disk 356 

37.  Dortmund  Tank  at  Chicago 409 

38.  Emscher  Tanks 424 

39.  Covered  Septic  Tank  at  Champaign 427 

40.  Septic  Tank  at  Biringham,  Ala.,  Intake 428 

41.  "        "      (t         "  "     Discharge  Weirs 428 

42.  Nozzle  for  Spraying  Square  Area 460 

43.  Sprinkling  Filter  at  Reading 461 

44.  Types  of  Sewage  Sprinkling  Nozzles 463 

45.  Distribution  Curves  of  Sprinkling  Nozzles 465 

46.  Sewage  Disposal  Plant  at  Marion,  O 486 


CONTENTS. 


TABLES. 

PACK 

1.  Population  and  Per  Capita  Water  Consumption  in  Different  Cities  ....  15 

2.  Persons  to  a  Dwelling,  by  States 18 

2a.  Persons  to  a  Dwelling  in  Several  Cities 19 

3.  Gaugings  of  Sewage  Flow,  Providence,  R.  1 22 

4.  Toronto,  Canada 23 

5.  "  "  "                 Schenectady,  N.  Y 23 

6.  "  "  "                 Atlantic  City,  N.  J 23 

7.  "  "  "                 Weston,  W.  Va.,  Insane  Hospital 24 

8.  "  "  "  and  Water  Consumption,  Des  Moines,  la.  27 

9.  Maximum  Rates  of  Rainfall 30 

10.  Relative  Cost  and  Capacity  of  Sewers,  Washington,  D.  C 42 

11.  Velocity  and  Discharge  in  Circular  Sewers,  4  to  36  in 48 

12.  "    '      "          "         "        "  ll    33  in.  to  10  ft 50 

T3-  Pt  a>  R>  Velocity  and  Discharge  for  Different  Depths  of  Sewage, 

Circular  Sewers 53 

14^  p,  a,  R,  Velocity  and  Discharge   for  Different  Depths  of  Sewage, 

Egg-shaped  Sewers 54 

15.  Materials  Moved  by  Different  Velocities  of  Water 58 

16.  Calculations  of  Sewer  Sizes  for  Minimum  Grades 118 

17.  Prices  and  Weights,  Vitrified  Clay  Sewer  Pipe 222 

18.  Prices  of  Drain-tile 221 

19.  '  *     ' '  Light-weight  Iron  Pipe 223 

20.  Amount  of  Cement  for  Laying  Different  Sizes  of  Sewer-pipe 223 

21.  Cost  of  Excavating,  Back-filling  and  Sheathing  Trenches 224 

22.  Cost  of  Laying  Sewer-pipe 224 

23.  Cost  of  Circular  Brick  Sewers 225 

24.  Cost  of  Manholes 226 

25.  Amount  of  Excremental  Organic  Matter  in  Sewage 368 

256.  Pounds  of  Organic  Matter  Per  Capita  Per  Day 368 

26.  Analyses  of  Sewage  of  Several  Cities 379 

266.  Analyses  of  Sewage  of  Several  Massachusetts  Cities 381 

27.  Results  of  Precipitation  of  Sewage  with  Various  Chemicals 412 

28.  Disinfection  of  Sewage  and  Effluents 471 

29.  Analyses  of  Sewage  Sludge 479 

30.  Purification  Plants  in  Ohio,  Description  and  Cost 489 

31.  Sewage  Treatment  Plants  in  the  United  States 49r 


v,  -  u  -w  UNIVERSITY 

OF 


SEWERAGE. 


CHAPTER  If 
THE    SYSTEM. 

ART.  1.     REQUIREMENTS  OF  A  SYSTEM. 

A  SYSTEM  for  the  removal  of  sewage  is  demanded  by  a 
populous  community  on  two  grounds:  the  higher  one  of  the 
public  health,  and  the  more  popular  one  of  convenience;  and 
in  designing  a  system  each  of  these  purposes  must  be  kept 
constantly  in  mind,  the  first  being  ever  given  predominance 
over  the  second  if  they  conflict  in  any  way.  The  proper 
meeting  of  these  demands  determines  the  principles  of 
designing. 

There  are  two  imperative  essentials  to  sanitary  sewerage: 

I.  That  the  sewage,  and  all  the  sewage,  be  removed  with- 
out any  delay  to  a  point  where  it  may  be  properly  disposed 
of. 

II.  That  it  be  so  disposed  of  as  to  lose  permanently  its 
power  for  evil. 

Convenience  requires  that  the  sewage  be  collected  and 
disposed  of  with  the  least  trouble  to  the  householder  and  in 
the  least  obtrusive  and  offensive  way. 

In  taking  up  the  study  of  sewerage  for  any  particular  place 
or  community  the  first  question  arising  is  that  of  the  general 


2  SEWERAGE. 

system  to  be  adopted.  In  many  cases  financial  limitations 
will  be  forced  upon  the  engineer  as  an  unfortunate  but  im- 
perative argument  in  the  choice  not  only  of  the  details  of  the 
system  but  even  of  the  system  itself.  He  must  perforce 
recognize  these  limitations  in  addition  to  the  requirements  of 
sanitation  and  convenience,  but  should  not  carelessly  assume 
that  since  there  is  but  little  money  to  spend  upon  the  work 
the  care  given  to  the  design  will  need  to  be  only  proportion- 
ately great.  He  should  realize  that  the  highest  talent  is 
needed  to  obtain  the  best  results  with  limited  resources. 

The  solution  of  the  difficulty,  when  a  complete  water- 
carriage  system  is  rendered  out  of  the  question  by  reason  of 
its  cost,  may  lie  in  the  construction  of  only  the  most  neces- 
sary portion  of  the  system  or  in  the  adoption  of  one  of  the 
dry-sewage  systems. 

ART.  2.    DRY  SEWAGE  METHODS. 

The  methods  in  common  use  for  removing  excrement  and 
liquid  house  wastes  may  be  divided  conveniently  into  three 
general  classes:  (i)  Dry  Sewage,  (2)  Pneumatic,  and  (3)  Water- 
carriage  systems. 

The  most  primitive  method  of  application  of  excrements 
to  the  soil — if  it  can  be  called  a  method — would  be  embraced 
under  the  first  head.  The  old-fashioned  privy  was  a  step 
forward,  and  in  a  large  part  of  this  country  is  as  yet  the  only 
one  which  has  been  taken,  privacy  being  the  main  argument 
for  its  adoption.  But,  while  contributing  somewhat  to  this 
and  to  comfort,  it  cannot  be  considered  as  a  sanitary  appli- 
ance. "  Constructed  for  the  avowed  purpose  of  retaining  the 
solid  matters  as  long  as  possible  upon  the  premises,  they 
become  centres  of  pollution  and  infection.  The  liquid  por- 
tions, escaping,  pollute  the  soil  and  neighboring  wells;  the 
noxious  exhalations  arising  from  their  putrefying  contents 
contaminate  the  air."  (Samuel  M.  Gray's  Report  on  Proposed 
Sewerage  System  for  Providence,  R.  I.). 


THE    SYSTEM.  3 

Regular  movement  of  the  bowels  is  essential  to  health  and 
to  bodily  and  mental  vigor.  Yet  a  rainy  day,  a  deep  snow,  or 
publicity  of  location  has  kept  many  a  person  from  the  daily 
attention  to  nature's  demands  when  this  requires  a  visit  to  the 
outdoor  privy. 

This  last  objection  is  met  by  the  indoor  closet  connected 
with  a  cesspool.  This  is  an  improvement  on  any  method  of 
exposed  deposits,  as  it  prevents  the  transportation  of  nocuous 
substances  therefrom  by  flies.  But  cesspools  should  be  made 
tight  and  be  cleaned  at  intervals. 

A  cesspool  8J  feet  in  diameter  and  10  feet  deep  to  which 
a  family  of  five  contribute  a  daily  average  of  25  gallons  of 
sewage  (a  low  estimate)  would,  if  tight,  require  to  be  cleaned 
twice  each  year.  Very  few,  it  is  believed,  are  cleaned  this 
often;  many  are  never  cleaned,  but  the  contained  liquid  leaches 
out  into  and  through  the  adjacent  soil,  which  soon  loses  its  power 
to  purify  it.  This  soil  pollution  is  the  most  serious  objection 
to  the  cesspool,  and  has  rendered  unsafe  the  waters  of  many 
private  wells  and  even  public  ones. 

Fresh  sewage  is  not  injurious  to  health  unless  taken  into  the 
stomach,  nor  is  it  very  offensive  to  the  smell;  but  from  putres- 
cent  excreta  and  kitchen  slops  come  those  noisome  gases  which, 
although  probably  not  themselves  bearers  of  malefic  germs, 
at  least  lower  the  vitality  and  render  the  body  more  vulnerable 
to  disease,  and  may  constitute  a  serious  nuisance.  Retained 
for  weeks  and  months  in  a  liquid  or  semi-liquid  state  in  a  cess- 
pool, sewage  is  then  under  the  conditions  best  adapted  to 
putrefaction  in  its  foulest  form.  Especial  pains  should  be  taken, 
therefore,  to  see  that  a  sufficient  outlet  be  always  open  for  the 
escape  of  these  gases,  such  as  by  the  continuation  of  the  soil 
pipe  above  the  roof,  or  by  a  special  vent  carried  above  the 
reach  of  snow. 

This  vilest  of  liquids  is  dangerous  in  two  ways:  it  may  reach 
and  taint  wells  for  hundreds  of  feet  around,  and  it  may 
pollute  the  air  existing  in  the  soil  under  cellars,  which  air  will 


4  SEWERAGE. 

exhale  and  permeate  the  houses  above.  In  excavating  for 
sewers  in  gravelly  soil  in  a  city  street  the  author  has  found 
the  gravel  colored  black  by  the  liquid  from  a  cesspool  located 
75  feet  distant  in  the  rear  of  the  house  opposite;  which 
liquid  must  consequently  have  passed  under  or  around  the 
cellar  of  this  house. 

The  general  adoption  of  the  septic  tank,  which  has  been 
called  the  "glorified  cesspool,"  cannot  properly  be  urged  as  an 
excuse  for  the  cesspool.  In  reality  the  two  differ  in  every 
essential.  In  no  satisfactory  septic  tank  does  the  sewage  remain 
longer  than  twenty-four  or  at  the  most  forty-eight  hours.  Even 
then  there  are  given  off  large  quantities  of  gases  which  no  one 
would  think  of  piping  into  his  house,  as  is  practically  done 
from  most  cesspools.  Moreover  the  use  of  cesspools  scatters 
a  large  number  of  centres  of  soil-pollution  throughout  a  closely 
populated  area. 

ART.  3.     DRY  SEWAGE  SYSTEMS. 

The  methods  already  referred  to  can  hardly  be  called 
systems,  but  are  rather  makeshifts.  The  simplest  systems 
which  can  be  at  all  commended  are  the  Pail  system  and  the 
Earth-closet.  These  are  used  but  little  in  this  country,  but 
would  be  for  many  small  villages  a  vast  improvement  over 
the  privy  or  cesspool. 

The  Pail  system  consists  essentially  of  the  placing  under 
the  privy-seats  of  pails,  which  are  to  be  removed,  emptied  in 
some  spot  where  a  nuisance  will  not  thereby  be  created, 
cleaned,  and  returned.  Duplicate  pails  must  be  provided  to 
be  used  in  place  of  these  during  their  absence. 

This  method  has  been  used  at  Marseilles,  Havre,  and  other 
French  cities;  at  Rochdale,  Birmingham,  Manchester,  and 
other  places  in  England;  but  only  in  certain  districts  of  these 
cities,  which  are  introducing  water  carriage  and  are  yearly 
increasing  the  territory  thus  sewered.  It  has  been  used  by 
a  few  communities  in  this  country  also,  among  them  Vine- 
land,  N.  J.,  Memphis,  Tenn.,  Atlanta,  Ga.,  and  Warren,  O., 


THE  SYSTEM. 


but  has  been  replaced  in  most  of  these  with  water-carriage 
systems. 

A  modification  of  and  improvement  upon  the  Pail  system 
is  the  Earth-closet  system,  in  which  pulverized  dry  earth, 
charcoal,  or  ashes  are  used  as  a  deodorizer  and  are  applied  to 
the  excreta  while  fresh,  the  mixture  being  subsequently 
removed,  preferably  as  in  the  Pail  system.  Brick-clay  and 
loam  rank  high  as  deodorizers  when  applied  in  a  perfectly 
dry  and  powdered  state.  Ashes  are  not  so  effective.  In 
Bremen  powdered  turf  is  used.  There  is  not  evident  a  suffi- 
cient superiority  in  charcoal  to  compensate  for  its  cost  and 
other  disadvantages. 

The  deodorizing-powder  should  be  applied  each  time  the 
closet  is  used.  An  excellent  arrangement  is  that  of  a  large 
box  or  barrel  resting  upon  an  extension  of  the  seat  and  with 
an  aperture  and  slide  so  contrived  that  any  desired  amount 
of  the  powder  may  be  deposited  upon  the  excrement  by  a 


frrrrr 


l 


18 


FIG.  i. — MODIFIED  BIRMINGHAM  PAIL. 

slight  motion  of  a  convenient  handle.  The  simplest  method 
of  applying  the  deodorizer  is  by  a  small  scoop  or  shovel,  the 
earth  being  kept  in  a  box  placed  in  a  convenient  position  in 
the  closet. 

For  either  the  Pail  or  Earth-closet  system  the  receptacle 
should  be  round,  as  this  form  is  more  easily  cleaned  than  a 


SEWERAGE. 

square  one;  and  preferably  of  metal,  as  a  wooden  pail  soon 
becomes  saturated  with  foul  liquors.  A  good  form  is  that 
of  the  modified  Birmingham  pail.  The  pails  should  be  thor- 
oughly cleaned  after  each  emptying,  and  a  thin  layer  of  earth 
should  be  spread  over  the  bottom  of  the  pail  when  it  is  re- 
placed under  the  seat. 

The  mixture  of  earth  and  excreta  may  be  dried  and  used 
again;  but  there  is  a  possible  danger  in  this,  since  bacteria 
are  not  often  destroyed  by  moderate  heat;  it  will  probably 
be  found  more  convenient  also  to  deposit  it  immediately  upon 
the  garden  or  field  as  a  fertilizer.  If  the  Pail  or  Dry-earth 
system  is  adopted  for  a  village  or  city  an  arrangement  may 
be  made  by  contract  for  removing  the  buckets  or  tubs  at 
intervals  of  not  more  than  a  week,  the  material  to  be  disposed 
of  by  the  contractor.  Such  disposition  of  it  should  be  made 
— either  by  placing  it  directly  upon  the  fields;  or  by  drying 
and  pulverizing  it,  in  which  form  (poudrette)  it  is  more  con- 
venient for  use  as  a  fertilizer;  or  by  burning  it  (see  Chapter 
II) — as  will  avoid  the  creating  of  a  nuisance  (see  Art.  10). 

There  are  several  methods,  some  patented,  for  disposing 
of  excreta  and  garbage  on  the  premises  by  means  of  heat, 
by  either  drying  or  cremating.  The  heat  for  these  is 
obtained  either  from  a  furnace  constantly  burning,  in  which 
case  its  use  in  summer  is  exceedingly  inconvenient  and  is 
usually  dispensed  with;  or  by  occasional  fires  lighted  at  long 
intervals,  during  which  the  waste  matter  undergoes  dangerous 
putrefaction.  On  account  of  these  and  other  equally  serious 
objections  these  methods  are  not  to  be  commended,  particu- 
larly since  the  cost,  were  every  house  to  adopt  them,  would 
in  most  locations  suffice  to  construct  an  excellent  water- 
carriage  system. 

These  dry-sewage  systems,  though  improvements  on  the 
privy  and  cesspool,  are  imperfect  from  a  sanitary  point  of 
view  in  that  they  require  the  excreta  to  be  stored  about  the 
premises  for  a  certain  period,  and  because  they  fail  to  pro- 


THE  SYSTEM.  7 

vide  for  the  removal  of  slops  and  sink-water  and  dispose  of 
urine  to  a  limited  extent  only.  Neither  do  they  provide 
for  the  drainage  of  the  soil  nor  for  the  removal  of  surface- 
water.  Convenience  also  is  not  fully  served  by  their  use. 

ART.  4.      PNEUMATIC  SYSTEMS. 

In  the  pneumatic  systems  the  faeces  only  are  removed, 
the  house  drainage,  surface  and  sub-soil  water  requiring  a 
separate  system  of  sewers  or  utilizing  the  gutters.  The  most 
widely  known  of  these  is  the  Liernur,  which  is  used  in  Amster- 
dam, Rotterdam  and  one  or  two  smaller  Holland  cities. 
This  system  is  practicable  under  certain  conditions  only  and 
will  not  be  described  at  length.  Its  object  is  to  remove  the 
sewage  at  frequent  intervals  through  pipes,  by  means  of  a 
vacuum,  to  a  central  station,  there  to  be  disposed  of  in  some 
way,  usually  by  being  manufactured  into  a  fertilizer.  The 
great  cost  of  this  system  is  prohibitive  to  its  introduction  into 
small  cities  and  towns,  and  on  account  of  its  limited  applica- 
bility, as  well  as  for  practical  and  sanitary  reasons,  its  adop- 
tion in  future  designs  is  improbable. 

The  Shone  system,  which  is  used  to  some  extent  in 
England  and  her  colonies  and  in  this  country,  although 
classed  among  the  Pneumatic  systems,  is  really  not  in  itself  a 
system,  but  an  application  to  the  water-carriage  system  of  a 
method  of  pumping  sewage  by  the  direct  action  of  com- 
pressed air.  It  will  therefore  be  considered  under  the  head 
of  the  Water-carriage  System. 

ART.  5.     WATER-CARRIAGE  SYSTEM. 

The  Water-carriage  system  has  now  been  so  almost  uni- 
versally adopted  where  any  improvement  upon  the  primitive 
privy  has  been  attempted  that  the  term  "  Sewerage  System  " 


8  SEWERAGE. 

is  ordinarily  used  without  further  qualification  to  refer  to  it. 
When  properly  constructed  and  managed  it  is  certainly 
deserving  of  its  popularity,  being  the  best  and  cheapest 
method  yet  contrived  for  the  removal  of  sewage. 

As  its  name  implies,  its  distinctive  characteristic  is  the 
removal  through  conduits,  by  gravitation,  of  sewage  which 
has  been  greatly  diluted  with  water.  It  meets  the  first 
principal  requirement  of  a  sanitary  system  (Art.  i) — it 
removes  all  house-wastes  and  removes  them  immediately.  It 
also  serves  the  secondary  but  by  no  means  unimportant  pur- 
pose of  removing  the  surface-water  and  draining  the  ground. 
Its  convenience  also  is  excelled  by  no  other  system.  More- 
over, where  the  territory  is  quite  thickly  populated — as  in 
the  average  town — it  is  in  the  end  cheaper  than  any  other 
system.  The  two  most  weighty  arguments  against  it  are  the 
large  amount  of  water  needed  for  its  efficient  working,  and 
the  pollution  of  streams  and  waste  of  the  valuable  manurial 
properties  in  the  sewage  when  this  is  emptied  into  river  or 
sea,  as  is  frequently  done.  Victor  Hugo  in  his  "  Les 
Mis£rables  "  devotes  a  long  chapter  to  the  "  Crime  of  the 
Century"  involved  in  this  waste.  But  whether  this  matter 
is  ultimately  wasted  or  its  use  by  man  only  deferred  it  is  not 
necessary  to  discuss.  The  all-convincing  argument  with  any 
but  the  sentimentalist  is  that,  while  there  may  be  manurial 
value  in  sewage,  no  commercially  profitable  method  of  utili- 
zing it  has  yet  been  found.  The  best  disposition  to  be  made 
of  it  is  therefore  that  which  is  least  harmful,  unpleasant,  and 
expensive,  and  in  most  cases  water  carriage  enables  us  to 
provide  such  disposition. 

The  argument  that  its  proper  working  involves  the  use  of 
large  quantities  of  water  is  undoubtedly  true.  But  where 
water-works  already  exist  this  objection  has  little  force — less 
in  this  country  than  abroad,  where  20  to  40  gallons  per  capita 
is  considered  a  liberal  allowance  for  water-consumption: 


THE  SYSTEM.  9 

while  in  this  country  our  small  cities  must  provide  two  or 
three  and  the  large  ones  five  or  six  times  this  amount,  which, 
with  in  many  cases  a  small  percentage  additional  for  flushing, 
is  usually  sufficient  and  no  difficulty  is  found  in  providing  it. 
Some  expense,  however,  is  frequently  incurred  for  flushing- 
water  and  to  this  extent  is  there  force  to  the  objection. 

Places  which  are  without  a  general  water-supply  or  the 
general  use  of  individual  supplies  are  barred  from  the  adop- 
tion of  the  Water-carriage  system.  For  such,  the  best  plan 
is  to  adopt  the  Earth-closet  system  until  such  time  as  water 
has  been  introduced  into  most  of  the  dwellings,  when  a 
Water-carriage  system  may  be  initiated,  the  Earth-closet 
pails  being  continually  relegated,  as  the  conduit  system  is 
extended,  to  the  outskirts  of  the  town,  where  the  growth  will 
probably  keep  a  year  or  two  ahead  of  the  water-supply  and 
sewer-construction. 

Other  objections  are  sometimes  raised  to  the  Water- 
carriage  system  which  are  either  equally  applicable  to  all 
systems  or  which  are  the  result  of  prejudice.  The  possibility 
of  the  introduction  into  dwellings,  through  the  house-connec- 
tions, of  sewer-air  (which  is  not  a  "  gas")  is  one  of  these, 
and  is  certainly  a  real  one.  But  the  resulting  danger  is  not 
so  great  as  that  connected  with  similar  evils  of  other  systems, 
and  it  is  preventable  by  careful  designing  and  construction  of 
the  sewers  and  house-plumbing. 

ART.  6.      COMBINED  AND  SEPARATE   SYSTEMS. 

The  Water  Carriage  system  has  been  adopted  generally 
in  all  civilized  countries  as  preferable  to  any  other  yet  devised. 
This  system  has  been  subdivided  according  to  construction 
and  use  into  the  Combined  and  the  Separate  systems;  the 
terms  "Combined"  and  " Separate"  referring  to  the  two 
classes  of  waters  which  it  is  desirable  to  remove — rain  water 


10  SEWERAGE. 

and  house  sewage.  In  the  former,  both  classes  of  water  are 
carried  in  a  common  conduit;  in  the  latter  the  house  sewage 
is  removed  through  small  sewers,  and  the  storm  water  through 
other  larger  ones  or  in  the  gutters,  or  partly  in  one  and  partly 
in  the  other. 

A  few  years  ago  there  was  a  rivalry  between  these  systems, 
but  it  is  now  generally  realized  that  there  are  conditions 
under  which  each  of  them  is  most  desirable,  and  in  many 
instances  a  judicious  combination  of  the  two  will  work  to 
better  advantage  than  either  alone.  Such  combination  is  re- 
ferred to  in  this  work  as  a  Compound  system. 

The  relative  advantages  of  the  two  classes  of  sewers  will  be 
treated  of  more  at  length  in  Chapters  II  and  VI.  They  may 
be  stated  briefly  as  follows:  The  small  house  sewers  of  the 
separate  system  give  a  greater  velocity  to  ordinary  amounts  of 
sewage,  and  consequently  cleaner  sewers,  than  do  the  larger 
combined  sewers.  This  smallness  of  size,  however,  has  the 
objection  that  it  renders  more  difficult  the  removal  of  any 
obstructions  or  sediment  which  may  collect. 

Where  a  complete  system  of  both  storm  and  house  sewers 
is  provided  in  the  separate  system  the  total  cost  is  greater 
than  that  of  a  system  of  combined  sewers  of  equal  capacity. 
This  additional  cost,  however,  is,  to  a  certain  extent,  offset  by 
the  fact  that  the  storm  sewers  can  frequently  be  placed  at  less 
depth  than  could  combined  sewers  which  must  carry  house 
sewage,  which  will  effect  some  reduction  in  cost.  The  fact 
that  towns  which  do  not  require  complete  storm  sewerage  or 
which  are  too  poor  to  afford  a  complete  system  of  separate 
sewers  can  obtain  the  more  necessary  removal  of  house  wastes 
at  much  less  expense,  is  of  great  advantage  in  permitting  an 
earlier  installation  of  the  latter  than  can  otherwise  be  possible. 

Objection  is  made  that  large  quantities  of  water  are  used 
for  flushing  the  pipes  of  the  separate  system.  But  if  the  sewers 
of  a  combined  system  are  kept  equally  as  clean,  much  larger 


THE    SYSTEM.  II 

quantities  of  water  would  be  required  for  the  same  purpose 
except  during  the  occasional  seasons  when  rain  storms  are 
frequent. 

The  occasional  claim  that  large  sewers  possess  the  ad- 
vantage that  they  can  be  laid  at  flatter  grades  than  small  ones 
is  incorrectly  advanced,  since,  as  a  matter  of  fact,  the  larger 
sewers  must  be  given  steeper  grades  to  secure  equal  velocity 
in  the  ordinary  dry  weather  flow. 

It  is  true  that,  where  the  separate  system  is  used,  surface 
water  is  frequently  allowed  to  run  for  long  distances  in  the  gutters. 
But  this  is  not  a  fault  of  the  system,  and  merely  indicates  that 
those  in  authority  consider  the  funds  available  to  be  more 
wisely  spent  in  providing  house  sewerage  than  complete  surface 
drainage,  the  latter  of  which  can  be  arranged  for  whenever 
desired,  if  the  designer  of  the  system  has  not  been  remiss. 

The  danger  of  house  traps  being  forced  if  adequate  venti- 
lation is  not  provided  is  less  when  large  sewers  are  used  than 
where  the  sewers  are  small.  But  such  ventilation  is  an 
essential  part  of  each  system,  which  there  is  no  excuse  for 
omitting.  The  removal  of  foul  air  can  be  effected  more 
completely  in  the  smaller  sewer,  but  is  somewhat  less  neces- 
sary in  the  large  one  of  equal  cleanness.  Much  more  im- 
portant is  the  fact  that  deposits,  which  are  the  cause  of  foul  sewer 
air,  are  more  likely  to  form  in  the  large  sewer  than  in  the  small 
ones. 

A  very  important  argument  in  favor  of  the  separate  system 
and  one  which  the  action  of  many  State  Health  Boards  is 
making  almost  imperative  in  their  respective  states,  is  the 
practical  necessity  for  its  use  where  a  treatment,,  of  the  house 
sewage  is  either  immediately  necessary  or  required  by  the 
authorities,  or  may  in  the  future  become  so.  It  is  true  that 
street  washings  are  often  as  foul  as  house  sewage  and  that 
purification  of  them  is  desirable;  but  there  are  few,  if  any, 
combined  systems  where  storm  water  is  purified,  and  the 


12  SEWERAGE, 

present  tendency  is  away  from  rather  than  toward   any  con- 
sideration of  such  purification. 

ART.  7.      SUMMARY. 

The  proper  conclusion  in  reference  to  the  system  to  be 
adopted  would  seem  to  be — the  water-carriage,  where  its  ex- 
pense is  not  prohibitive  and  the  dwellings  are  abundantly 
supplied  with  water.  If  the  cost  of  the  water  supply  is 
peremptorily  limited,  a  dry-sewage  system — preferably  the  dry 
earth — would  be  a  great  improvement  on  the  privy  or  other 
primitive  methods.  The  dry-sewage  system  is  described  at 
sufficient  length  in  this  chapter,  as  the  proper  conduct  of  it 
requires  little  else  than  cleanliness  and  faithful  attention.  The 
disposal  of  sewage  thus  collected  will,  however,  be  referred  to 
in  Part  IV. 

The  water-carriage  system  is  more  complicated  in  design, 
in  construction,  and  in  operation;  and  to  the  consideration  of 
this  system  the  remainder  of  this  work  will  be  devoted,  y 


CHAPTER  II. 
AMOUNT   OF  SEWAGE. 
ART.  8.     FACTORS  IN  THE  CALCULATION. 

THE  object  of  a  system  of  sewers  is  in  general  to  conduct 
all  excreta  and  fouled  waters  from  the  places  of  their  origin 
to  an  appointed  outlet,  and  as  rapidly  and  continuously  as 
possible.  No  part  of  the  sewage  should  be  retained  in  any 
portion  of  the  system  for  any  considerable  time,  either  in  its 
liquid  form  or  in  the  shape  of  deposits  upon  the  bottoms  or 
walls  of  the  conduits  or  their  appurtenances;  for  such  reten- 
tion may  permit  of  putrescence  of  the  organic  matter  before 
it  reaches  the  place  assigned  for  disposal,  the  conduits  thus 
becoming  no  better  than  "  elongated  cesspools."  The  insur- 
ing of  this  result  with  the  greatest  certainty  and  economy  is 
the  prime  requisite  in  the  design  of  a  sewerage  system. 

The  largest  part  of  the  system  is  made  up  of  conduits  of 
various  size,  shape,  grade,  material,  and  depth  below  the 
ground-surface.  The  two  last  are  practical  points  to  be  con- 
sidered later  (Articles  32  and  40),  but  the  size,  shape,  and 
grade  are  to  be  determined — approximately  at  least — by 
theoretical  considerations.  The  data  used  in  these  considera- 
tions are  (i)  the  amount  and  character  of  the  sewage  to  be 
removed,  and  (2)  the  relative  surface  elevations  and  grades 
along  the  line  of  the  proposed  sewer-conduit.  The  latter 
are  obtained  by  the  instrumental  field-work,  to  be  discussed 
in  Chapter  V.  While  the  grade  of  the  sewer  need  not  be 

13 


14  SEWERAGE. 

that  of  the  street-surface,  it  cannot  depart  far  from  this  with- 
out greatly  increasing  the  difficulty  and  cost  of  construction. 
The  two  grades  will  therefore  be  approximately  parallel 
unless  very  good  reasons  to  the  contrary  exist. 

ART.  9.     AMOUNT  OF  HOUSE-SEWAGE. 

The  obtaining  of  satisfactory  figures  for  the  amount  of 
sewage  is  one  of  the  most  difficult  tasks  entering  into  the 
designing  of  a  system.  The  sewage  to  be  considered  is  of 
two  entirely  different  kinds,  from  two  totally  different 
sources:  house-sewage  from  dwellings,  stores,  factories,  and 
other  buildings,  and  storm-water  from  the  streets,  the  ground- 
surface,  and  from  roofs.  The  former  is  limited  in  quantity 
largely  by  the  number  of  inhabitants  and  industrial  establish- 
ments and  the  water  contributed  to  the  sewers  by  each. 
The  latter  is  limited  by  nature's  local  limit  of  intensity  of 
rainfall,  the  area  tributary  to  the  sewer,  and  the  proportional 
run-off. 

Considering  first  the  house-sewage,  this  is  almost  entirely 
composed  of  water  which  has  first  been  introduced  artificially 
into  the  dwellings  or  establishments.  Excreta  and  solids 
legitimately  finding  their  way  to  the  sewer  comprise  only  a 
very  small  part  of  the  sewage — from  5  to  15  parts  in  10,000. 
There  may  be  besides  this  comparatively  small  amounts  of 
leakage  of  ground-water,  roof-water,  and  flushing-water 
reaching  the  sewer.  It  would  seem,  therefore,  that  we  may 
make  a  close  approximation  to  the  amount  of  house-sewage 
by  using  the  water-consumption  of  the  town  in  question. 
This  can  usually  be  obtained  from  the  pumping  records,  or, 
in  the  case  of  a  gravity  supply,  from  a  meter  set  in  the  main 
near  the  reservoir.  Table  No.  I  shows  the  rates  for  a  num- 
ber of  cities  of  the  United  States  at  intervals  of  10  years. 
This  table  shows  the  great  difference  between  the  per  capita 


AMOUNT  OF  SEWAGE. 
TABLE  No.  1. 


1870. 

1880. 

1890 

Cities. 

Population. 

Per  Capita 
Consumption. 

Population. 

Per  Capita 
Consumption. 

Population. 

Per  Capita 
Consumption. 

New  York  City  

Q42,  2Q2 

QO  2 

1,206,590 

78  7 

1,515,301 

79 

Chicago,  111.    .  .    
Philadelphia    Pa  .... 

298,977 
674.,  O22 

62  32 
ce    ii 

503,304 

847,542 

114.0 
68.1 

1,099  650 
I  046,964 

138 
131 

Brooklyn    N    Y.    ... 

3Q6  OQQ 

47.16 

566,689 

54.2 

806,143 

72 

St    Louis    Mo  

310,864 

3C    08 

346,000 

72.1 

451,770 

72 

250,526 

DO.  IS 

4l6,OOO 

02.  0 

448,477 

80 

216,236 

40  o 

256,708 

75-9 

296,908 

112 

Cleveland    O 

Q2  82Q 

W  2J. 

61.0 

261,3^3 

IO3 

Buffalo    NY    

117  714. 

^s  08 

1  06  o 

255,664 

1  86 

70  577 

O"4  24 

118  ooo 

152.0 

205,876 

161 

TOO   7  5  "3 

29  o 

c2  O 

161  129 

74. 

88,150 

78 

Paterson,  N.  J  

78,347 

128 

4Q    1  ao 

3O  I 

74,398 

20 

70,028 

64 

Troy   N.  Y  

60,956 

125 

50,093 

55 

Erie    Pa  

40,634 

112 

30,217 

83 

20  056 

22 

18,060 

IQ4 

Keokuk    la  

14,  101 

78 

Brookline    Mass 

12   IO3 

T\ 

Baton  Rouge    La  .  .  • 

10  478 

IQ 

IO.O44 

IQQ 

rates  in  different  cities.  It  also  shows  in  each  city  an  increase 
of  from  10%  to  100%  in  consumption  during  each  decade. 
Neither  the  increase  of  per  capita  consumption  nor  the  dif- 
ference in  rates  of  increase  in  the  various  cities  seems  to 
follow  any  law,  except  that  the  former  shows  a  constant 
advance.  It  might  be  expected  that  the  per  capita  con- 
sumption would  be  greater  in  cities  where  there  was  consider- 
able manufacturing  or  many  well-kept  lawns  than  where  these 
conditions  did  not  exist;  and  this  is  the  general  rule — with 
many  exceptions,  however.  Also  large  cities  usually  have  a 
higher  rate  than  small  ones;  but  this  rule  also  has  many 
exceptions. 


1 6  SEWERAGE. 

For  each  particular  case  the  daily  consumption  should  be 
obtained  from  the  water-works  record,  or,  if  there  are  no 
records  of  consumption  for  that  locality,  a  careful  selection 
should  be  made  of  the  per  capita  consumption  of  a  city  whose 
conditions  closely  resemble  those  of  the  place  in  question. 
From  these  the  per  capita  rate  will  be  obtained.  In  order  to 
be  on  the  safe  side  the  present  rate  should  be  increased  by  at 
least  25$  to  allow  for  a  probable  increase  in  consumption, 
since  the  construction  must  serve  not  only  the  present  popu- 
lation, but  that  of  the  next  30  or  more  years. 

If  meters  are  used  on  a  majority  of  the  services  a  great 
reduction  in  the  consumption  can  be  effected — from  30$  to 
60$  in  most  instances. 

Unless  water-meters  have  become  generally  established 
and  accepted,  however,  no  allowance  should  be  made  for  the 
reduction  in  sewage  due  to  their  use  unless  the  average  daily 
rate  exceeds  100  gallons  per  capita.  There  is  no  reason  for 
a  daily  rate  exceeding  this  amount,  and  the  present  tendency 
is  to  meter  supplies  before  they  reach  this  point.  An  allow- 
ance of  100  gallons  will  be  made  in  calculations  in  this  work, 
as  being  a  safe  one  for  any  but  exceptional  cases. 

The  average  daily  consumption,  however,  "  is  not  uniform 
throughout  the  year,  but  at  times  is  greatly  in  excess  of  the 
average  for  the  year  and  at  other  times  falls  below  it.  It 
may  be  20%  or  30$  in  excess  during  several  consecutive 
weeks,  50$  during  several  consecutive  days,  and  not  infre- 
quently 1 00$  in  excess  during  several  consecutive  hours.'* 
(J.  T.  Fanning,  "  Water  Supply  Engineering.")  Many  water- 
works engineers  use  75$  excess  as  an  average.  This  gives 
for  a  maximum  flow,  on  a  basis  of  100  gallons  daily,  a  rate 
of  175  gallons  per  capita  daily  =  .1215  gallons  per  minute  = 
.00027  cubic  feet  per  second. 

It  must  be  most  urgently  insisted,  however,  that  each  case 
should  be  studied  by  itself  in  the  light  of  all  the  data  avail- 


AMOUNT  OF  SEWAGE.  17 

able.  These  figures  are  given  as  approximate  averages  only, 
to  be  used  in  designing  when  no  local  records  exist.  It 
should  also  be  borne  in  mind  that  the  consumption  given  is 
an  average  including  that  used  in  manufacturing  and  for  all 
other  purposes.  These  last  constitute  a  very  uncertain  por- 
tion of  the  whole,  but  unless  there  were  definite  figures 
obtainable  it  would  not  be  safe  to  reduce  the  average  by 
more. than  25%  to  obtain  a  rate  for  residences  only.  As  the 
assumed  maximum  rate — 175  gallons — was  but  a  roughly 
estimated  average,  it  may  be  used  unchanged  for  residential 
districts;  and  where  factories  are  to  be  provided  for  a  study 
should  be  made  of  the  processes  employed  in  them  in  order 
that  a  close  approximation  may  be  made  to  the  amount  of 
sewage  to  be  expected  from  each. 

The  amount  of  house-sewage  from  buildings  (other  than 
waste  water  from  factories  and  water-motors)  which  will  reach 
any  particular  sewer  is  generally  considered  to  be  a  function 
of  the  number  of  persons  contributing  to  this  amount.  For  a 
district  or  city  this  number  may  be  obtained  in  two  ways 
— by  estimating  the  ultimate  number  of  residences  and 
assigning  a  certain  number  of  occupants  to  each,  doing  the 
same  with  factories,  stores,  and  other  buildings;  or  by 
estimating  the  probable  ultimate  population  per  acre  for 
different  sections  of  the  city.  The  former  is  the  more  accu- 
rate for  built-up  sections;  the  latter  sufficiently  so  for  un- 
developed territory  or  that  which  will  probably  undergo  a 
change  in  the  character  of  its  buildings. 

For  use  in  calculating  by  the  first  method  the  table  on  the 
following  page,  adopted  from  the  U.  S.  census  of  1900,  is  given. 

There  are  in  each  city  certain  districts  in  which  the 
population  is  much  more  dense  than  is  indicated  by  this 
table.  One  hundred  persons  in  one  dwelling  is  not  an  excep- 
tional rate  in  certain  portions  of  New  York  City.  For  an 
ordinary  residence  district  six  persons  to  each  dwelling  is  a 
sufficient  average.  In  factories  and  stores  which  do  not  use 


i8 


SEWERAGE. 


TABLE  No.  2. 

PERSONS  TO   A  DWELLING,  BY  STATES. 


State. 

1900. 

1890. 

1880. 

The  United  States  

C.  7 

C.  C 

=5.6 

North  Atlantic  Division  

c.o 

">-Q 

6.0 

M^aine 

4-  7 

4    0 

c    2 

New  Hampshire 

4.8 

4-0 

51 

Vermont 

4.5 

4.8 

c   o 

Massachusetts        .                             

6.2 

6.3 

6\ 

Rhode  Island     

6.3 

6.6 

6"7 

Connecticut.  _  

c.7 

c.7 

c.7 

New  York 

7-O 

6  7 

6  6 

New  Jersey 

c.n 

5  8 

r   Q, 

Pennsylvania 

c    i 

ET.  7 

c    C 

South  Atlantic  Division 

C.2 

c.4 

r    r 

Delaware 

4.8 

^.O 

e   4 

Maryland                                             .        

c.4 

c.7 

6  a 

District  of  Columbia                  .        

2 

5-6 

c.o 

6.2 

Virginia  

C.2 

c.7 

e.7 

West  Virginia  

C.7 

5-6 

C.T 

North  Carolina 

C.  "2 

c.4 

e   ? 

South  Carolina 

C    2 

C.  2 

%    2 

Georgia 

^•1 

c.4 

f    7. 

Florida                                                     

4.7 

^.O 

C.    I 

North  Central  Division                                  

5.0 

C.2 

tr.  t 

Ohio  

4.8 

C.I 

c.c; 

Indiana  

4.6 

4-8 

C.  7 

Illinois 

r.7 

c.  7 

c   7 

Michigan 

4-6 

4.8 

c   i 

^^isconsin                          »                                .  .  .  . 

C.2 

C.7 

c    e 

Minnesota                                            

c.c 

c.7 

r;   7 

Iowa                                                    

4.8 

c.o 

e  4 

Missouri 

1.2 

C      C 

5Q 

North  Dakota  

5.0 

4^8 

1    *          A 

South  Dakota 

4-Q 

4.8 

y*4-6 

Nebraska                                                         .    . 

c.o 

C.  7 

C.     -2 

Kansas                                                         

•      4.7 

4-Q 

c    •? 

South  Central  Division                      

C.  I 

c.  c 

C.  C 

Kentucky  

C.2 

5-5 

«;.8 

Tennessee 

C.  2 

f     C 

c  6 

Alabama                                                          .... 

^.o 

c.4 

e    7 

Mississippi                                               

^-O 

c.  c; 

r    4 

Louisiana                                 

C.  I 

c.  c 

c   4 

Texas     

C.3 

c.6 

c   c 

Indian  Territory  

•5-2 

Oklahoma                                                              .  . 

4.  7 

4    I 

Arkansas                                                        

<.  I 

c.4 

e    4. 

^Vestern  Division                         

4-7 

^.O 

e    i 

Montana                    

4-  "> 

4-0 

4    3 

Wyoming  ,  

4-7 

C.I 

4   0 

Colorado  

4-5 

5.1 

C.O 

New  M^exico                            .               ........ 

4    3 

4.4 

A       C. 

Arizona             

4    3 

4.  "> 

4.    'J 

Utah  

e.  2 

5-6 

C,   4 

Nevada  

•2.Q 

4-  "> 

4    ^ 

Idaho                                                    

44 

4   7 

42 

\Vashington                      

4   n 

c.  i 

4    8 

Oregon 

4-  7 

C.  I 

c    4 

California  

4-  7 

C.  I 

c.4 

Alaska  

6.0 

Hawaii  

4-8 

Dakota  Territory. 


AMOUNT  OF  SEWAGE. 


TABLE  No.  2a. 

PERSONS  TO  A  DWELLING  IN   SEVERAL  CITIES. 


City. 

Population 
in  1900. 

Persons  to  a  Dwelling. 

1900. 

1890. 

1880. 

New  York  * 

3,217,182 
287,104 

175,597 
163,752 

80,865 

133359 
50,167 

52,733 
62,139 
29,282 
34,i59 

17.0 

5-4 
7-0 

5-8 
5-3 
4-9 
4.6 

5-4 
4-9 
4-9 
4-9 

15-6 

5-6 
7-5 
5-7 
5-5 
5-9 
4-8 
5-7 
5-° 
5-5 
5-i 

14.0 
6.0 
7-4 

^5 
6.1 

6.7 

5-2 

5-7 
5-4 
5-1 
5-6 

New  Orleans   La 

Providence    R  I 

Kansas  City,  Mo.                   

Nashville,  Tenn            

Denver,  Colo  

Harrisburg,  Pa  

Erie,  Pa  

Des  Moines,  la  

Sacramento,  Cal  

Springfield,  111  

*  Manhattan,   Bronx  and   Brooklyn  boroughs  only. 

water  for  manufacturing  purposes  the  maximum  hourly  rate 
per  capita  of  occupants  is  not  nearly  as  great  as  in  the  case  of 
residences;  a  maximum  rate  of  20  gallons  per  day  will  be 
sufficient  allowance  for  ordinary  cases,  being  contributed  by 
water-closet  flushes,  urinals,  and  wash-basins.  One  person 
to  each  50  square  feet  of  floor-space  may  be  taken  as  a 
maximum  density  for  factories  and  office-buildings. 

A  method  frequently  used  is  that  of  adding  a  percentage 
of  increase  to  the  present  population  of  each  city  or  section. 
American  towns  under  50,000  population  have  been  found  as 
a  general  rule  to  double  in  size  in  about  15  or  20  years. 
Having  ascertained  for  each  case  its  past  rate  of  increase  and 
present'  population,  these  are  taken  as  the  basis  for  calcula- 
tions. But  this  increase  is  far  from  uniform  over  the  entire 
area  of  a  town,  differing  in  different  sections;  also,  after  a 
section  has  reached  a  certain  density  of  population  it  remains 
practically  stationary,  unless  its  character  change — as  from 
residential  to  business  or  manufacturing.  This  should  be 
considered  in  calculating  district  populations;  but  the  per- 
centage of  total  growth  of  a  town  may  be  used  as  a  check 
upon  the  sum  of  the  populations  assumed  for  the  various  sec- 


20  SEWERAGE. 

tions.  The  law  of  increase  varies  in  different  cities,  but  that 
followed  in  the  past  by  the  one  under  consideration,  having 
been  obtained  from  the  records,  can  be  projected  into  the 
future,  it  being  assumed  that  this  law  will  remain  constant. 

Considerable  judgment  must  be  used  in  locating  division- 
lines  between  sections  and  assigning  to  each  its  density  of 
ultimate  population.  The  most  hilly  sections  will  probably 
be  least  thickly,  and  those  in  the  level  bottom  lands  most 
thickly,  populated.  Further  than  this  it  would  be  unsafe  to 
try  to  state  any  general  law.  The  least  population  which 
should  be  assigned  to  any  habitable  section  within  city  limits 
is  20  per  acre.  The  per  acre  population  in  any  residence 
section  can  be  expressed  by  the  equation 

~ 

in  which  /  =  the  average  length  of  a  city  block ; 

b  =    "        "        breadth"  "    "       " 

o  =    "  number  of  occupants  of  each  lot; 

/=    "        "  "        "    front  feet  to  a  lot; 

</  =    "        *'        depth  of  a  lot; 

w—    "        "        width  of  a  street; 

P=    "  population  per  acre. 

For  a  section  where  the  blocks  are  400  ft.  by  200  ft., 
streets  66  ft.  wide,  lots  50  ft.  by  100  ft.,  and  the  population 
residential  (o  =  6), 

43560  X  4QQ  X  200  X  6 

~  50  X  ioo[400  X  200  +  66(400  -[-  200  +  66)]  " 

For  a  tenement  district,  each  building  on  a  lot  50  ft.  by 
100  ft.  and  containing  on  an  average  80  occupants,  P  would 
equal  453,  which  is  about  P  for  the  Tenth  Ward,  New  York 
City. 

A  block  with  lots  25  feet  by  80  feet  and  with  6  occu- 
pants each  represents  fairly  well  the  most  dense  residence 


AMOUNT   OF  SEWAGE.  21 

section  of  an  average  city  of  10,000  to  100,000  population. 
This  gives  P=  85.  In  many  cities  the  maximum  does  not 
exceed  50  per  acre. 

The  population  found  times  .00027  for  residences  and 
times  .00003  for  factories  and  office-buildings  (on  the  basis  of 
the  previously  assumed  daily  consumption)  will  give  in  cubic 
feet  per  second  the  maximum  amount  of  house-sewage  from 
buildings  to  be  expected.  To  this  must  be  added  manufac- 
turing wastes,  which  are  to  be  allowed  for  in  quantities  which 
must  be  decided  upon  separately  for  each  individual  case. 
Also  if  the  soil  is  inclined  to  be  wet  at  a  depth  less  than  that 
of  the  proposed  sewer  (and  this  includes  a  larger  proportion 
of  localities  than  most  persons  realize)  an  additional  allowance 
must  be  made  for  ground-water  leaking  through  the  joints 
With  care  this  need  not  amount  to  more  than  one  cubic 
foot  per  second  for  each  30  to  100  miles  of  sewer;  but  it  has 
been  known  under  most  unusual  conditions  to  more  than 
equal  the  entire  capacity  of  the  system.  (The  average  leakage 
of  137  miles  of  8-inch  to  36-inch  sewer  in  Boston,  was  found 
to  be  .06  cubic  feet  per  second  per  mile;  and  double  this  in 
the  spring.) 

Where  flush-tanks  are  used  (see  Chapter  IV)  an  additional 
allowance  is  frequently  made  for  water  from  them.  But  this 
seems  entirely  unnecessary,  since  their  very  purpose  is  to  tem- 
porarily gorge  the  sewer  for  as  great  a  distance  as  possible; 
and  the  smaller  the  sewer  the  better  is  this  mission  fulfilled. 
The  average  discharge  per  minute  of  100  tanks,  each  dis- 
charging 300  gallons  once  in  24  hours,  would  amount  to  only 
ij%  of  the  capacity  of  a  1 5-inch  sewer  at  minimum  grade. 

ART.  10.  DATA  OF  HOUSE-SEWAGE  FLOW. 
Instead  of  using  rates  of  water-consumption  as  equivalent 
to  the  sewage  discharge  it  would  undoubtedly  be  preferable 
to  establish  the  actual  relation  between  these,  based  upon  the 
rate  of  flow  of  sewage  itself  in  various  towns  already  sewered. 
But  very  few  such  records  exist — too  few  to  enable  us  to 
deduce  a  definite  law  from  them  with  certainty,  although  a 


22 


SEWERAGE. 


study  of  even  these  few  is  instructive.  One  of  the  first 
extended  series  of  gaugings  of  sewage  discharge  made  in 
America  were  those  of  the  Providence  (R.  I.),  sewers  by  Sam- 
uel M.  Gray.  A  condensed  summary  of  them  and  of  other 
gaugings  is  given  in  the  following  tables: 

TABLE  No.  3. 

SUMMARY    OF    RESULTS    OF    WEIR      MEASUREMENTS    OF    SEWAGE    FLOW 

IN    PROVIDENCE,    R.    I. 
(Condensed  from  a  Report  by  SAMUEL  M.  GRAY  on  the  Sewerage  of  Providence.) 


Street. 

Houses 
Connected. 

Population 
Connected. 

Average 
Discharge 
per  Second. 

Maximum 
Discharge 
per  Second. 

Date  of 
Measurement. 

Dor  ranee  ..... 

772 

6562 

7.  -22 

1  1  65 

j  Average  of 

Brook 

C7C 

AlSo 

5  O2 

6  78 

i  May  and  June 
Sat     Feb    2 

c   OI 

6  78 

Mon      "        4 

•i  085 

547 

Tues     July  I 

3  88 

5.47 

Thurs      "    3 

3-86 

5.76 

Sat.,         "    5 

4  28 

54.7 

Mon         "    7 

Elm     

III4 

8800 

A     JC 

7  QO 

"      Jan    28 

3.69 

7.QO 

Tues       "     20 

« 

3.317 

6.32 

Wed.,  June  4 

< 

•5.37 

6.32 

Fri.,         "     6 

« 

7.IO 

c  ii 

Thurs  ,    "     19 

N   Main  

2.57 

4  4s? 

Mon.,  May  12 

2.46 

3.80 

Wed.,      "     7 

(i 

1.76 

-I   2C 

Fri     July  25 

1.50 

1  2O 

Mon.  ,  Feb.  i  T 

« 

2.40 

c.4O 

Thurs.,    "     14 

tt 

2.30 

4.82 

Sat.,        "    16 

<  « 

2.06 

2  65 

Mon.        "    18 

(i 

2.106 

3  2O 

Fri.,         "    29 

Ives  

204 

1814 

0.753 

.02 

Mon.,  March  3 

0.854 

.38 

Wed.,      "       5 

« 

0.605 

.30 

Mon.,  Aug.  25 

« 

0.600 

O.Q2 

Wed.,     "      27 

College        .... 

108 

824 

1.05 

82 

Fri.,  May  2 

1.  07 

.81 

Mon.,  "        5 

321 

2720 

1.57 

3.82 

j  Mean  for  May 

Power     

31 

23Q 

0.26 

O.56 

I      6-21 
Wed.,  April  23 

o  26 

O  54 

Fri.           "      25 

« 

0.045 

O.I4 

"     Aug.  22 

Nash      

2C 

icn 

O.O37 

o.  135 

Mon.,  April  21 

O.O3O 

O.O6O 

Tues.,      "     22 

« 

0.036 

0.086 

Aug.  6,  7,  ii 

Park  

21 

162 

O.O34 

0.187 

Fri.,  April  18 

« 

O.O43 

0.385 

Mon.,  Aug.  18 

Martin  

153 

1178 

1.  2O8 

I.4OO 

Wed.,  July  9 

Pitman  

86 

655 

I.2O2 

2.380 

Mon.,  April  28 

.«« 

0.744 

1.380 

Wed.,       "     30 

AMOUNT   OF  SEWAGE. 


TABLE  No.  4. 

GAUGINGS    MADE    IN    TORONTO,    CANADA,    IN     THE     SPRING    OF    1891, 
LASTING    THREE    DAYS. 


Popula- 
tion per 
Acre. 

Total 
Popu- 
lation. 

Discharge. 
Gallons  per 
Head  per 

Popula- 
tion per 
Acre. 

Total 
Popu- 
lation. 

Discharge. 
Gallons  per 
Head  per 

Popula- 
tion per 
Acre. 

Total 
Popu- 
lation. 

Discharge. 
Gallons  per 
Head  per 

Day. 

Day. 

Day. 

15-7 

39>OI4 

77 

I7.6 

6,160 

101 

41.7 

1  1  ,  300 

68 

46.2 

17,186 

133 

42  3 

11,125 

69 

9-4 

7.23? 

105 

8.8 

3,168 

83 

39-8 

6,368 

"3 

45-7 

14,21-= 

•        89 

44.0 

572 

316* 

42-4 

8,268 

89 

38.3 

19,265 

53 

45-5 

4.595 

77 

u.  8 

8,732 

IO2 

24.0 

87 

41.8 

1,045 

U3 

43-7 

9.832 

89 

*  No  explanation  given  for  this  high  average. 

TABLE  No.  5. 

GAUGINGS    MADE    IN  SCHENECTADY,  N.  Y.,  WEDNESDAY,  FEBRUARY  5, 

AND  THURSDAY,  FEBRUARY  6,  1892 — HOURLY  FOR  24  HOURS. 
(Fifteen  miles  of  sewers,  about  1500  house-connections  tributary  to  the  point 
where  gaugings  were  made.  Before  house-connections  were  made  a  seepage 
of  60,000  gallons  per  day  was  measured.  There  was  also  50,000  gallons  of 
water  contributed  daily  by  flush-tanks.  These  two,  or  110,000  gallons  per  day, 
have  been  deducted  from  the  total  hourly  flow  in  obtaining  the  quantities  in  the 
table.) 

WEDNESDAY,    FEBRUARY    5,    1892. 


Hour 

9AM 

10 

1  1 

12  M 

I   P  M 

2 

o 

Total  flow  per  hour  .  . 

35,217 

38,769 

32,892 

32,892 

34,049 

35,217 

36,490 

34  049 

Hour           

E;  P.M 

6 

7 

8 

IO 

II 

12 

Total  flow  per  hour  .  . 

32,892 

31,840 

31,840 

31,840 

29,301 

29,301 

29,301 

28,135 

THURSDAY,    FEBRUARY   6. 


Hour IIAM.         2     |       3  4  5  6(7  8 

Total  flow  per  hour. ..(28, 135  28, 135)  25,71 1128.135]  26. 833!  26,833  29,461  31,840 


Average  flow  per  hour,  31,213  gallons;  minimum  flow,  25,711  gallons;  max- 
imum flow,  38,769  gallons,  or  24$  increase  over  the  average. 

TABLE  No.  6. 

WATER-CONSUMPTION     AND     SEWAGE     FLOW,    ATLANTIC     CITY,    N.    J., 

DECEMBER,   1 89I-NOVEMBER,   1892. 

(Average  Daily  Percentage  of  Excess  of  Water  Consumed  over  Sewage 
Pumped — by  Months.) 


« 

g 

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g 

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rt 

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£ 

32 

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53 

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18 

Kf> 

Excess  of  water-tans  over  sewer-connertions    percentage   . 

18 

The  average  daily  percentage  of  excess  for  the  year  = 
The  average  excess  of  water-taps  for  the  year 


24  SEWERAGE. 

TABLE  No.  7. 

RESULT  OF  A  GAUGING  BY  WEIR  MEASUREMENT  OF  THE  FLOW  OF 
THE  MAIN  OUTFALL  SEWER  OF  THE  STATE  INSANE  HOSPITAL 
AT  WESTON,  W.  VA.,  IN  JANUARY,  1891. 

(Made  by  GEO.  W.  RAFTER.  Condensed  from  "Sewage  Disposal  in  the 
United  States."  Self-closing  fixtures  were  used  in  the  building.  10,000  gallons 
per  day,  or  7  gallons  per  minute,  of  water  of  condensation  from  the  steam- 
heating  apparatus  was  discharged  into  the  sewer.) 


Rate  in 

Rate  in 

Rate  in 

Rate  in 

Day. 

Hour. 

Gallons 
per  Min. 

Day. 

Hour. 

Gallons 
per  Min. 

Day. 

Hour. 

Gallons 
per  Min. 

Day. 

Hour.  Gallons 
per  Min 

12 

78.75 

IA  M. 

44-55 

I  P.M. 

99-45 

IA.M.      34  65 

I  P.M 

93-60 

2 

44-55 

2 

86.40 

2 

34.65 

2 

93.60 

3 

44-55 

3 

93.60 

3 

39-60 

3 

75.60 

4 

44-55 

4 

75.60 

4 

49-05 

4 

75.60 

5 

49-  05 

5^, 

5 

93.60 

5 

49-05 

a 

5 

70.20 

rt 

6 

64  So 

rt 

6 

81.00 

6 

58.50 

'O 

V) 

6 

75.60 

I 

7 

75.60 

1 

7 

93-00 

X 
tt 

7 

7O.2O 

s 

7 

75  60 

3 

8 

86.40 

a 

8 

58.50 

T> 

8 

86.40 

1 

8 

70.20 

H 

9 

105.30 

t_ 

9 

53-55 

fc 

9 

105.30 

1 

9 

58.50 

10 

117.90 

10 

53-55 

10 

86.40 

10 

53-55 

ii 

93.60 

ii 

44-55 

n 

86.40 

ii 

44-55 

12 

93.60 

12 

44-55 

12 

105.30 

12 

44-55 

The  flow  of  the  Compton  Avenue  sewer,  St.  Louis,  Mo., 
was  gauged  hourly  from  March  15  to  23,  1880.  The  mini- 
mum flow  measured  was  88  gallons  per  minute,  the  maximum 
203  gallons,  and  the  mean  132  gallons. 

A  gauging  of  the  College  Street  sewer,  Burlington,  Vt., 
taken  at  15-minute  intervals  from  7.30  A.M.  to  10.30  P.M. 
gave  two  maximums,  one  at  7.45  A.M.,  the  other  at  9  A.M.; 
these  were  each  140  gallons  per  minute.  The  minimum  flow 
was  65  gallons,  the  mean  115  gallons.  Fifty-four  houses 
were  connected;  the  tributary  population  was  325. 

Gaugings  made  at  Memphis,  Tenn.,  for  one  day  gave  a 
maximum  of  80  gallons  and  a  minimum  of  35  gallons  per 
minute. 

Gaugings  made  at  Kalamazoo,  Mich.,  in  1885,  from 
I  A.M  to  12  midnight  on  Monday,  March  9,  gave  a  minimum 


AMOUNT  OF  SEWAGE. 
Plate  No.  I. 


4,000,000 
3,000,000 
2,000,000 
1,000,000 


4,000,000 
3,000,000 
2,000,000 
1,000,000 


4,000,000 
3,000,000 
2,000,000 
1,000,000 


5,000,000 
4,000,000 
3,000,000 
2,000,000 
1,000,000 


5,000,000 
4,000,000 
3,000,000 
2,000,000 
1,000,000 


EAST  SIDE  SEWER 

WEST    ««  <• 

BOTH  SEWERS  COMBINED 

WATER  CONSUMPTION 


26  SEWERAGE. 

flow  of  224  gallons  per  minute,  a  maximum  of  287  gallons, 
and  a  mean  of  254  gallons. 

Gaugings  were  made  at  Des  Moines,  Iowa,  from  June  30 
to  July  16,  1895,  by  J.  A.  Moore  and  W.  J.  Thomas,  class 
of  '95,  Iowa  Agricultural  College  (see  Plate  I).  The  sewerage 
system  at  the  outlet  of  which  the  gaugings  were  taken  com- 
prised: on  the  west  side  235,000  feet  of  sewers,  contribu- 
tary  population  19,400,  15  hydraulic  elevators;  on  the  east 
side  29,000  feet  of  sewers,  contributary  population  8100,  3 
hydraulic  elevators. 

These  were  combined  sewers.  Rain  fell  on  two  Sundays 
only,  and  is  indicated  by  the  unusual  height  of  the  curve. 
Water-meters  were  used  on  the  services;  water  was  supplied 
to  33»7°°  persons,  but  the  amount  consumed  by  each  was 
not  ascertained,  the  average  consumption  for  the  city  being 
taken.  The  diagram  for  the  west  side  shows  noon-hour  stops 
of  factories.  The  high-water  curves  for  July  10,  11,  12,  and 
13  were  caused  by  the  water  company  flushing  dead-ends 
outside  of  the  limits  of  the  sewers  gauged.  On  the  I2th  the 
large  flow  in  the  west-side  sewer  was  probably  caused  by  a 
part  of  this  flushing-water  reaching  it. 

The  maximum  dry-weather  rate  of  flow  on  the  west  side 
was  at  10.15  A.M.  Friday,  July  12 — 175.3  gallons  per  capita. 

The  maximum  dry-weather  rate  of  flow  on  the  east  side 
was  at  6.30  P.M.  Tuesday,  July  2 — 142  gallons  per  capita. 

The  minimum  dry-weather  rate  of  flow  on  the  west  side 
occurred  at  4  A.M.  Saturday,  July  6 — 23.2  gallons  per  capita. 

The  minimum  dry-weather  rate  of  flow  on  the  east  side 
occurred  at  4.30  A.M.  Friday  July  5 — 22.5  gallons  per  capita. 

The  average  dry-weather  rate  of  flow  on  the  west  side  was 
66  gallons  per  capita. 

The  average  dry-weather  rate  of  flow  on  the  east  side  was 
74  gallons  per  capita. 

Table  No.  8  gives  the  water  pumped  and  the  sewage  dis- 


AMOUNT   OF  SEWAGE. 


27 


TABLE  No.  8. 


Date. 

Water. 

Sewage. 

8i.6#  of  the 
Water  Pumped. 

Remarks. 

July  3 

2,720,000 

2,200,000 

2,2ig,520 

4 

1,829  000 

1,330,000 

,4g2,464 

Holiday 

5 

2.352,635 

2,050,000 

,  9^,750 

6 

2,750,205 

2,040,000 

.244,167 

7 

i,  8og.no 

1,115,000 

,476,234 

Sunday;  rain 

8 

2,379,820 

2,030,000 

,941,933 

g 

2,437,325 

2,O2O,OOO 

,g8g,265 

charged  during  the  seven  days  when  the  measurements  taken 
were  apparently  reliable.  The  first  column  gives  the  total 
amount  of  water  pumped:  the  second,  the  total  sewage  flow; 
the  third,  81.6$  of  the  first  column,  that  being  the  proportion 
between  the  number  of  water-taps  and  that  of  the  sewer-con- 
nections. The  close  correspondence  between  the  two  last 
columns  shows  what  an  excellent  index  the  water-consump- 
tion furnishes,  in  this  town  at  least,  of  the  total  house-sewage 
to  be  expected.  July  12  was  the  only  date  when  the  maxi- 
mum flow  of  the  west  side  exceeded  125  gallons  per  capita, 
and  then  for  two  hours  only.  The  average  for  this  side  was 
66  gallons.  Disregarding  the  maximum  of  the  I2th  instant, 
which  was  due  to  hydrant-flushing,  we  have  a  maximum  for 
this  side  89$  greater  than  the  average ;  and  for  the  east  side 
the  maximum  was  92$  above  the  average.  The  record, 
however,  covers  two  holidays  out  of  the  seven,  making  the 
average  unusually  low;  also  the  general  average  for  that  time 
of  year  would  ordinarily  be  lower  than  that  for  an  entire  year. 
These  gaugings  seem  to  point  uniformly  to  the  conclusions 
already  stated — that  the  winter  flow  of  sewage  is  greater  than 
the  summer;  that  the  maximum  and  minimum  flow  do  not 
ordinarily  vary  from  the  yearly  average  more  than  75%,  but 
frequently  do  by  50%;  that  the  house-sewage  per  capita  very 
nearly  equals  the  water-consumption  where  the  taps  and  sewer- 
connections  are  equal  in  number. 


28  SEWERAGE. 

The  engineer  must  select  and  use  with  a  great  deal  of 
judgment  all  the  data  obtainable  in  fixing  upon  the  quantities 
which  the  sewer  should  be  designed  to  carry.  The  method 
of  making  the  calculations  will  be  explained  more  at  length 
in  Chapter  VI. 

ART.  11.     AMOUNT  OF  STORM-WATER. 

The  amount  of  storm-water  reaching  a  given  sewer 
depends  upon  the  rate  of  rainfall,  the  time  during  which  this 
rate  is  continued,  the  proportion  of  the  rainfall  which  flows 
off,  and  the  time  taken  by  a  raindrop  after  falling  to  reach 
the  point  under  consideration.  This  last  depends  upon  the 
shape,  extent,  and  nature  of  the  surface  over  which,  and  the 
length  and  grade  of  the  sewer  through  which,  it  must  flow. 

ART.  12.     RATES  OF  RAINFALL. 

It  is  apparent  that  the  rate  at  which  the  water  reaches  the 
sewer  depends  to  a  greater  or  less  degree  on  the  rates  of  rain- 
fall from  minute  to  minute,  and  not  upon  the  amount  falling 
in  a  day  or  even  in  an  hour.  Records  giving  rainfalls  for 
these  latter  units  of  time  are,  therefore,  valueless  to  the 
sewerage  engineer.  Gauges  are  in  use  which  automatically 
register  the  rate  of  rainfall  at  each  moment  of  a  storm; 
and  so  great  a  necessity  for  such  records  has  been  felt  that 
the  use  of  self-registering  rain-gauges  is  becoming  more  and 
more  general,  and  in  most  of  the  large  cities  continuous  record 
of  the  rates  of  rainfall  is  obtained  either  by  a  city  department 
or  by  the  United  States  Weather  Bureau. 

Since  the  maximum  amount  of  water  to  be  removed 
determines  the  size  of  the  sewer,  we  are  concerned  only  with 
the  maximum  rates  or  those  near  the  maximum.  Rates  of 
heavy  rainfalls  for  various  cities  of  the  United  States  are 


AMOUNT   OF  SEWAGE.  29 

given  in  Table  No.  9.  Where  possible  several  high  rates 
during  the  same  or  consecutive  years  are  given  for  each 
locality,  but  no  attempt  has  been  made  to  give  a  record  of 
all  severe  storms  for  any  one  place  or  year.  An  examination 
of  rainfall  data  covering  many  years  shows  that  in  New 
England  a  rate  of  3.6  inches  an  hour  continuing  for  5  minutes 
may  be  expected  every  year  or  two,  a  rate  of  2  inches  con- 
tinuing for  20  minutes,  a  1. 5-inch  rate  continuing  for  30 
minutes,  and  i  inch  in  60  minutes.  In  New  York  State 
the  rate  may  be  about  20$  and  in  Pennsylvania  about  30$ 
higher.  In  Baltimore  and  Washington  we  may  expect  a 
5-inch  rate  for  5  minutes,  a  4-inch  rate  for  10  minutes,  a 
2.7-inch  rate  for  20  minutes,  a  2-inch  rate  for  30  minutes, 
and  1.4  inches  in  60  minutes.  In  New  Orleans  a  5.5-inch 
rate  for  5  minutes,  a  4.5-inch  rate  for  10  minutes,  a  3-inch 
rate  for  20  minutes,  a  2.5-inch  rate  for  30  minutes,  a  2-inch 
rate  for  60  minutes  or  even  more  may  be  expected.  In  the 
central  States  a  rate  of  3.7  inches  for  10  minutes,  2.8  inches 
for  20  minutes,  2.3  inches  for  30  minutes,  and  1.7  inches  in 
60  minutes  may  be  expected.  Further  data,  however,  may 
require  a  change  in  any  of  these  values. 

Prof.  Talbot  gives  as  a  formula  of  maximum  rates  of  rain- 
fall m  the  eastern  part  of  the  country,  r  —  — — ,  which 

*    i    1 5 

agrees  quite  closely  with  Plate  IV  S.  Atlantic  States  up  to  30 
minutes,  but  gives  too  small  values  for  longer  periods. 

The  records  seem  to  show,  where  any  information  on  the 
subject  is  given,  that  the  maximum  intensity  usually  lasts 
but  a  few  minutes,  seldom  more  than  ten;  that  it  sometimes 
occurs  at  the  beginning  of  a  storm,  but  in  a  great  majority  of 
instances  occurs  at  the  middle  or  end  of  it,  quite  a  number 
stopping  10  to  20  minutes  after  the  maximum  rate  is 
attained.  As  to  the  area  simultaneously  covered  by  the 
maximum  rates  of  fall,  almost  no  data  are  available. 


SEWERAGE. 


TABLE  No.   9. 

MAXIMUM    AMOUNTS    OF    RAIN    FALLING    DURING  DIFFERENT  PERIODS 

OF    TIME. 


Length  of  Period  in  Minutes. 

Place  and  Date. 

5 

10 

15 

20 

25 

30 

45 

60 

Over  60. 

Amt. 

Dura- 
tion. 

0.50 

5-2° 

24  h. 

Boston,  Oct.  12,  1895 
u         j-  1879-1891 

July  18,  1884 
Providence,  R.  I.,  May  18,  1877 
Aug.  29,  1877 
"        6,  1878 
"      28,  1882 
Ithaca,  N.  Y.,  Aug.  4,  ^92.    Preceded  by 
5  hours  of  light  rain 
Mt.  Carmel,  N.  Y.,  July  2,  1897 
Morrisania,  Oct.  30,  1866 
New  York  City,  Sept.  19,  1894 
Aug.  19,  1893 
7  times  during  1869-1891 
«        3    u           i>          ,.      .. 

o   fin 

1.50 

2  =;6 

5-03 
*'73 
I.  it 

ith. 
it  h. 
2h. 

o-35 

....jo.iki 

1.30 

.... 

1.50 

.... 



sleo 
6.17 

24  hV 

24  h. 

•        May  4,  1893 
1882             [sewer) 
'                 'July  6,    1896.    (Gorged   a 
Brooklyn,  N.  Y. 
Spring  Mount,  Pa.,  June  6,  1893 
"    during  1893  (4  storms) 
Philadelphia,  Pa.,  2  times  during  1884-1891 

:      ::  3  ;:    ;;    -  ;; 

March,  1890 
Baltimore,  1896 

Wash  ngton,  D.  C.,  2  times  during  1871-1891 

o  80 

2    60 

.          'l    00 

0.25  i  .00 

T  ""H 

1.50 
i  60 

.... 

o-45 

.... 







....  0.40 

0.21  0.35 

0.25  o  60 

O.8o  I    60 
....0.80 

U  f^ 

o!46 
0.85 

o!s8 
0.92 

o.6a 

0-95 

0.96 
0.64 

0^83 

0-95 



1.30 

.... 

i  50 

3-40 
3-19 
2.70 
2.32 



"       10       "                 "              "         " 

"     mean  of  many  rains 
New  Orleans,  June  17,  1895 
Aug.  13,  1894 
July  4, 
'  I4> 
Sept.,  1889  (2  storms) 
April  24,  1894.   Preceded   by 
6  hours  of  light  rain 

(.Jacksonville,  Fla.,  U.  S.  Weather  Bureau, 
f     1896 

1  Galveston,  Texas,  1896.      U.  S.  Weather 
j      Bureau 
Chicago,  once  during  1889-1891 
2  times    " 

"              2          "              "              "              " 

Ohio  Valley,  Tuly  16,  1896 

•  52 
.50 
•40 
.40 
.60 
•  as 

•35 

*4 

•3° 
.07 

10 

.30 

o'.Ss 
0.70 
o-75 
i  .20 
0.60 

o-75 

1.20 

I  .OO 
1.20 
1.50 
I.  00 

i.  "48 

l'£ 

I-75 
1.17 

,.78 

i'.ei 

'•95 

2.OO 

1-25 

2.05 

1.87 
2-'5 

2.10 

2.00 
2.70 
2.62 

2-45 

2.  2O 

6.00 
3-3° 

2-35 

"2*  hY 
•  h. 

'i*  h. 

,  60 

0.65 

0.20 

0.61 
0.26 
0.30 
o-45 

0.00 

0.47 
0.70 
0.44 

o  37 
°-57 

1-15 

0.85 
0.92 
0.77 
0.47 
0.65 

1.40 

0.90 
!.*> 

0.82 
0.62 
0.77 

i-55 

I    01 

i-57 
0.91 
0-75 
0.90 

i.78 

1.71 
1-15 

1.50 

0.88 

I.  10 

1.88 

1.99 
i.  80 





i  .00 
1-23 



o  80 

o  60 

2  h.'  ' 

1  .75 

0.28 
0.04 
0.15 
0.38 
0.25 
0.06 
°«35 

o'58 

0.19 
0-45 
0-57 
0.50 

o  33 

3-3^ 

2h. 

St.  Louis,  May  14,  1891 
Cleveland,  Ohio,  1896  "1 

Detroit,  Mich.,        "     1U.  S.  Weather 
"           "                     "     Bureau 
Little  Rock,  Ark.,  || 

San  Diego,  Cal.,  December,  1896 
"ampo,  Cal.,  August,  1891 
Palmetto,  Nev.,     "        1890 

[•  Island  of  St.  Kitts 

0.88 
0.49 
0.85 
063 
0-75 
0.46 

1-13 

0.79 

I.  00 

0.91 
o-95 
0.60 

1.23 
1.04 
1.07 

'•13 
0.99 
0.66 

•38 
•3» 
•14 
•30 
.02 
.70 

i-73 

1.70 

1.78 

0.79 

0.91 
0.82 

"•5+ 

8.8 

36'  + 

12    + 

'24  hY 

2  h. 

A  MO  UN  7    OF  SEWAGE.  31 

ART.   13.     RUN-OFF  DATA. 

The  data  concerning  rates  of  run-off  as  compared  with 
rainfall  during  the  same  time  are  very  meagre.  The  total 
annual  or  monthly  proportion  of  run-off  has  been  ascertained 
in  many  different  localities,  but  even  this  is  for  natural 
wooded  surfaces  or  fields  only.  The  number  of  careful  gaug- 
ings  in  this  country  of  rainfall  within  city  limits  and  of  con- 
temporaneous sewer  discharge  from  a  known  area  probably 
does  not  exceed  a  half  dozen. 

An  extensive  and  scientific  gauging  was  that  made  at 
New  Orleans  in  1894-5  under  the  direction  of  the  Engi- 
neering Committee  on  Drainage.  Unfortunately  for  its 
general  usefulness  in  the  study  of  run-off  problems,  the 
run-off  measured  probably  included  seepage  from  a  soil 
lower  than,  and  consequently  more  or  less  saturated  by, 
the  Mississippi  River.  The  rainfall  was  recorded  contin- 
uously at  several  points  throughout  the  city,  and  several  of 
the  maximum  rates  are  given  in  Table  No.  9.  A  continuous 
record  was  also  kept  of  the  amount  of  water  reaching  the 
drainage-ditches  from  above  and  beneath  the  surface  of  the 
soil.  From  data  thus  and  otherwise  obtained  the  committee 
prepared  curve-diagrams  (Plate  No.  II)  for  the  calculation  of 
run-off  from  areas  of  different  extent,  character,  and  grade  of 
surface  in  New  Orleans.  "  The  set  marked  A  represents  the 
run-off  from  densely  built-up  parts;  the  set  marked  B  applies 
to  the  areas  having  small  yards,  or  a  medium  density  of 
population;  the  set  marked  C  applies  to  the  sparsely  built-up 
parts,  or  those  having  large  yards;  and  the  set  marked  D 
applies  to  the  rural  areas.  These  curves,  therefore,  indicate 
the  maximum  rate  of  rainfall  which  it  is  proposed  to  provide 
for,  and  which  is  assumed  to  reach  the  drains  and  canals  from 
the  respective  areas. 

11  They  do  not  warrant  the  assumption,  however,  that  the 


32  SEWEKAGE. 

discharge  will  never  exceed  the  quantities  given  for  it;  in  fact 
it  is  certain  that  they  will  be  exceeded,  but  at  such  rare  and 
indefinite  intervals  that  their  consideration  is  not  justified.  It 
should  also  be  remarked  that  the  curves  are  based  upon  the 
assumption  that  .  .  .  the  water  enters  the  drains  promptly, 
as  is  the  case  in  most  other  cities."  (Report  of  the  Engireer- 
ing  Committee — B.  M.  Harrod,  Henry  B.  Richardson,  and 
Rudolph  Hering — on  the  Drainage  of  the  City  of  Ne\\' 
Orleans;  1895.) 

A  number  of  gaugings  have  been  made  in  Washington, 
D.  C.,  in  districts  whose  streets  are  almost  entirely  paved 
with  asphalt.  In  one  case  "  the  flow  in  the  sewer  rose 
almost  immediately  after  the  rain  began  and  fell  to  its  normal 
level  within  a  few  minutes  after  the  rain  ceased."  During 
another  storm  "  at  its  maximum  period  the  rain  fell  for  37 
minutes  at  the  rate  of  0.9  of  an  inch  per  hour.  The  sewer- 
gauge  rose  to  a  height  of  3.7  feet,  giving  about  0.47  of  the 
capacity  of  the  sewer  and  indicating  no  loss  whatever  by 
absorption  or  evaporation  during  the  time  of  maximum  flow." 
(Hoxie  on  "  Excessive  Rainfalls,"  Transactions  Am.  Soc. 
C.  E.,  vol.  XXV.)  This  sewer  received  the  drainage  of  200 
acres. 

Gaugings  made  in  Rochester  by  Emil  Kuichling  are  too 
extensive  to  be  quoted  here,  but  the  tables  may  be  found  in 
the  Transactions  Am.  Soc.  C.  E.,  vol.  XX,  pages  1-60, 
accompanied  by  an  excellent  discussion  on  the  subject  of  run- 
off. The  conclusions  drawn  from  these  by  the  author  of  that 
paper  are  quoted,  as  stating  clearly  the  general  principles  on 
which  are  founded  the  rational  methods  of  calculating  run-off. 
The  gaugings,  he  says,  "  point  unmistakably  to  the  following 
general  conclusions: 

"  I.  The  percentage  of  the  rainfall  discharged  from  any 
given  drainage-area  is  nearly  constant  for  rains  of  all  consider- 
able intensity  and  lasting  equal  periods  of  time.  This  cir- 


AMOUNT  OF  SEWAGE. 


33 


Plate  II. 
MAXIMUM  FLOW  FROM  DRAINAGE  AREA  IN  CUBIC  FEET  PER  SECOND 


34  SEWERAGE. 

Lumstance  can  be  attributed  only  to  the  fact  that  the  amount 
of  impervious  surface  on  a  definite  drainage-area  is  also 
practically  constant  during  the  time  occupied  by  the  experi- 
ments. 

"  2.  The  said  percentage  varies  directly  with  the  degree 
of  urban  development  of  the  district,  or,  in  other  words,  with 
the  amount  of  impervious  surface  thereon.  .  .  . 

"  3.  The  said  percentage  increases  rapidly,  and  directly 
or  uniformly  with  .the  duration  of  the  maximum  intensity  of 
the  rainfall,  until  a  period  is  reached  which  is  equal  to  the 
time  required  for  the  concentration  of  the  drainage-waters 
from  the  entire  tributary  area  at  the  point  of  observation; 
but  if  the  rainfall  continues  at  the  same  intensity  for  a  long 
period,  the  said  percentage  will  continue  to  increase  for  the 
additional  interval  of  time  at  a  much  smaller  rate  than  pre- 
viously. This  circumstance  is  manifestly  attributable  to  the 
fact  that  the  permeable  surface  is  gradually  becoming  satu- 
rated and  is  beginning  to  shed  some  of  the  water  falling  upon 
it;  or,  in  other  words,  the  proportion  of  impervious  surface 
slowly  increases  with  the  duration  of  the  rainfall. 

"  4.  The  said  percentage  becomes  larger  when  a  moderate 
rain  has  immediately  preceded  a  heavy  shower,  thereby  par- 
tially saturating  the  permeable  territory  and  correspondingly 
increasing  the  extent  of  impervious  surface. 

"  5.  The  sewer  discharge  varies  promptly  with  all  appre- 
ciable fluctuations  in  the  intensity  of  the  rainfall  and  thus 
constitutes  an  exceedingly  sensitive  index  of  the  rain  and  its 
variations  of  intensity. 

"  6.  The  diagrams  also  show  that  the  time  when  the  rate 
of  increase  in  the  said  percentage  of  discharge  changes 
abruptly  from  a  high  to  a  low  figure  agrees  closely  with  the 
computed  lengths  of  time  required  for  the  concentration  of  the 
storm-waters  from  the  whole  tributary  area,  and  hence  the 
said  percentages  at  such  times  may  be  taken  as  the  proportion 


AMOUNT   OF  SEWAGE.  35 

of  impervious  surface  upon  the  respective  areas."  (Transac- 
tions Am.  Soc.  C.  E.,  vol.  XX,  page  37.) 

"  The  Nagpoor  (India)  storage  reservoir  receives  the 
flow  from  a  watershed  of  6.6  square  miles.  With  a  very 
absorbent  natural  surface  that  watershed  has  nevertheless 
delivered  to  the  reservoir  in  170  minutes  98$  of  a  downpour 
upon  its  entire  area  of  2.2  inches  in  80  minutes,  when  the 
power  of  absorption  of  the  soil  had  been  satisfied."  (Hoxie). 

Many  instances  could  be  named  where  storm-sewers  which 
were  designed  to  carry  a  run-off  of  one  cubic  foot  per  second 
have  caused  serious  damage  by  their  too  small  capacity; 
several  where  even  a  capacity  of  two  cubic  feet  per  second 
was  insufficient.  (One  inch  of  rainfall  per  hour  equals  one 
cubic  foot  per  second  per  acre  almost  exactly.)  Not  many 
years  ago  a  sewer  was  considered  by  most  engineers  to  be  of 
ample  size  if  it  was  designed  for  a  rainfall  of  one  inch  per 
hour,  one  half  running  off;  but  the  insufficiency  of  this  rule 
has  been  learned  by  costly  experience. 

Accounts  of  accidents  through  insufficient  sewer  dimen- 
sions are  unfortunately  more  numerous  than  data  giving  exact 
figures  of  unusual  volumes  of  rainfall  reaching  sewers. 

An  analysis  of  the  available  data  seems  to  point  to  the 
following  conclusions: 

That  the  total  run-off  from  any  area  is  directly  propor- 
tional to  the  imperviousness  of  the  surface,  and  that  this 
imperviousness  increases  with  the  length  of  the  storm,  unless 
it  is  already  100$. 

That  very  nearly  100^  of  the  water  falling  upon  an  im- 
pervious surface  flows  immediately  to  the  sewer  unless  held 
back  by  obstructions  in  the  street,  roof-gutters,  or  sewer- 
inlets — the  last  including  insufficiency  of  size  of  the  inlet.  A 
small  percentage,  however,  is  usually  evaporated  at  once;  and 
another  modicum  is  retained  upon  the  surface  in  slight  depres- 
sions. 


36  SEWERAGE. 

That  the  proportion  of  the  rainfall  on  any  given  imper- 
vious area  which  reaches  any  particular  point  in  the  sewer 
system  increases  with  the  length  of  the  storm  up  to  the 
time  when  the  run-off  from  the  most  distant  part  of  said  area 
reaches  the  point  of  observation;  after  which  the  run-off  very 
nearly  equals  the  rainfall  upon  said  area  while  the  rate  of  fall 
remains  constant. 

That  the  percentage  of  imperviousness  of  the  surface  may 
vary  from  o%  to  100%,  being  the  first  in  the  case  of  vary 
porous  soil  under  natural  conditions  at  the  beginning  of  a  rain, 
and  approximating  the  last  in  an  urban  district  where  streets, 
sidewalks,  and  yards  are  all  paved,  or  occasionally  where  a 
dense  clay  soil  is  saturated  by  previous  rainfall. 

Kuichlmg,  in  1909,  in  a  discussion  before  the  American  So- 
ciety of  Civil  Engineers,  gave  the  following  as  the  range  of 
estimated  values  of  imperviousness  (ratio  of  run-off  to  rain- 
fall) at  times  of  maximum  discharge: 

For  roof  surfaces  assumed  to  be  water  tight 7=0.70  to  0.95 

For  asphalt  pavements  in  good  order 0.85  to  0.90 

For  stone,  brick,  and  wooden  block  pavements  with 

tightly  cemented  joints 0.75  to  0.85 

For  same  with  open  or  uncemented  joints 0.50  to  0.70 

For  inferior  block  pavements  with  uncemented  joints  0.40  to  0.50 

For  macadamized  roadways o.  25  to  0.60 

For  gravel  roadways  and  walks o.  15  to  0.30 

For  unpaved  surfaces,  railroad  yards  and  vacant  lots  o.io  to  0.30 
For  parks,  gardens,  lawns,  and  meadows,  depending 

on  surface  slope  and  character  of  subsoil 0.05  to  o. 25 

For  wooded  areas  or  forest  land,  depending  on  surface 

slope  and  character  of  subsoil o.oi  to     . 20 


ART.   14.      FORMULAS  FOR  STORM-WATER  RUN-OFF. 

Many  attempts  have  been  made  to  construct  a  simple 
general  formula  for  obtaining  the  run-off  from  any  area.  The 
best  known  of  these  are  as  follows: 


AMOUNT  OF  SEWAGE.  37 


8L2 
Craig:  D  =  44oBNhyp.  log  -— . 

£> 

D  =  discharge  in  cubic  feet  per  second; 
L  =  extreme  length  of  drainage-area; 
5  =  mean  breadth  of  drainage-area; 
N= constant  varying  from  0.37  to  1.95. 

M 
Dredge:  Q  ==  1300^. 

L=  length  of  watershed; 
M  =  area  in  square  miles. 

^Dickens:  D  =  825^*. 

D  =  discharge  in  cubic  feet  per  second; 
M— drainage  area  in  square  miles. 

Fanning:  Q  =  2ooM". 

Q  =  discharge  in  cubic  feet  per  second; 
M  =  drainage-area  in  square  miles. 


^Burkli-Ziegler:          Q  =  I 

c=  constant — 0.75  for  paved  streets,  0.31  for  macadamized  streets; 
R  =  average  rate  during  heaviest  fall  in  cubic  feet  per  second  per  acre; 
5  =  general  fall  of  area  per  1000; 
Q= cubic  feet  per  second  per  acre  reaching  sewers; 
A  =  drainage-area  in  acres. 

/    N2    \6 

Kirkwood:  D  =  (-      -    . 

\  5  80457 

D  =  diameter  of  sewer  in  feet. 
5= sine  of  inclination. 
N  =  number  of  acres  in  area. 
Maximum  rainfall  of  one  inch,  one  half  running  off. 

3  log  A  +  log  N  +  6.8 
Hawksley:          log  D  =  -  — , 

D  —  diameter  of  sewer  in  inches; 
A  =  number  of  acres  to  be  drained; 
N=  length  in  feet  in  which  sewer  falls  one  foot. 
City  or  suburban  surfaces. 


SEWERAGE. 


Adams : 


logD  = 


2  log  A  +  log  N  -  3.79 


A  =  area  in  acres; 
.ZV=as  in  Hawksley; 
D  =  diameter  in  feet. 
For  one  inch  rainfall,  one  half  running  off. 


McMath : 


Terms  as  in  Burkli-Ziegler;   R  taken  at  St.  Louis  as  2.75. 

Kuichling:  Q  =  Aat(b-ct). 

Q=  discharge  in  cubic  feet  per  second; 
A  =  drainage-area  in  acres; 
/=  duration  in  minutes  of  the  intensity  (b  —  ct)', 

£=2  -j  for  Rochester,  N.  Y.     (Kuichling  recently  gives  as  a  for- 

_  t      mula  representing  storms  of  the  second  class  at  Rochester: 

J  r=i2/t-o6,  in  which  r=  rates. in  inches  per  hour.) 
_  proportion  of  impervious  surface 

The  following,  known  as  Roe's  tables,  gives  the  number 
of  acres  of  urban  surfaces  which  can  be  drained  by  sewers  of 
different  diameters  and  at  different  grades.  It  is  not  at  all 
reliable  and  is  no  longer  in  general  use. 


Inclination,  Fall,  or  Slope 


Inner  Diameter  or  Bore  of  Sewer  in  Feet. 


of  Sewer. 

2 

•i 

3 

4 

5 

6 

7 

8 

9 

10 

Level. 
i  in.  in  10  ft.,  or  :  480.  .  . 
i"  ••  «•  •«  •   :24o.... 

39 
43 
50 
63 
78 
90 
H5 

67 
75 
87 
H3 
M3 
165 
182 

120 

135 
155 
203 

257 
295 
318 

277 

308 

355 
460 

59° 
670 

730 

570 
630 

735 
950 

1200 

1385 
I5OO 

IO2O 

1117 

I3l8 
1692 
2l8() 
2486 
2675 

1725 
I925 
2225 

2875 
3700 
4225 
4550 

2850 
3025 
3500 
4500 
5825 
6625 
7125 

4125 
4425 
5100 

6575 
7850 

5825 
6250 

7175 
9250 
11,050 

i|"  ••«««•   :8o  

The  formulas  of  Craig,  Dredge,  Dickens,  and  Fanning 
apply  to  natural  surfaces  and  have  the  shape  and  extent  of 
the  drainage-area  as  the  only  variables.  The  Burkli-Ziegler, 
Kirkwood,  and  McMath  formulas  take  into  account  also  the 
slope  of  the  surface.  The  Burkli-Ziegler  and  Kuichling  allow 
for  varying  conditions  of  surface,  and,  together  with  the 
McMath,  for  varying  rates  of  rainfall.  All  these  formulas 
except  the  three  last  mentioned  are  based  on  an  assumed 
maximum  rate  of  rainfall. 


AMOUNT   OF  SEWAGE. 


39 


Roe's  tables  give  the  diameter  of  sewer  necessary  to  meet 
various  conditions  of  area  and  sewer  grade.  As  in  a  level 
sewer  the  surface  of  the  water  must  have  some  fall  if  there  is 
to  be  any  flow,  the  quantities  given  for  a  level  grade  can 
apply  only  to  a  limited  length  of  sewer.  None  of  these 
formulas  is  satisfactory  for  all  cases,  because  none  takes  into 
account  all  the  variable  conditions.  Those  which  are  prob- 
ably the  most  frequently  used  are  the  Burkli-Ziegler, 
McMath,  and  Ktiichling,  and  these  are  seen  to  be  the  ones 
containing  the  most  variables.  The  proper  test  of  any 
formula  is  to  calculate  by  it  from  known  data  quantities 
which  are  also  known.  Many  such  tests  of  all  these  formulas 
have  been  made,  and  it  has  been  found  that  there  are  few,  if 
any,  cases  in  which  all  will  give  results  practically  identical  or 
equal  to  the  actual  quantities  as  measured.  Such  a  compari- 
son is  given  of  Roe's  tables,  Hawksley's,  Kirkwood's,  and 
Biirkli-Ziegler's  formulas,  and  the  actual  gaugings  of  a  sewer 
in  Washington  made  in  1884  (from  paper  by  Capt.  R.  L. 
Hoxie  read  before  the  Am.  Soc.  C.  E.  July  2,  1886): 


Rainfall. 

Roe's  Tables. 

Hawksley. 

Kirk  wood. 

Burkli- 
Ziegler. 

Actual 
Maximum 
Flow. 

0.5"  in  15  min.  .  .  . 

36.3 

43-2 

51-7 

137-6 

300 

0-55"  in  37  min.. 

363 

43-2 

51-7 

61.9 

1  80 

The  discrepancies  are  largely  due  to  the  causes  already 
referred  to — that  factors  are  taken  as  constants  which  are 
really  variables,  and  hence  each  formula  can  give  correct 
results  for  certain  cases  only.  In  most  the  constant  is  sup- 
posed to  be  derived  from  maximum  rates  of  rainfall,  but  such 
data  were  until  recently  incomplete  and  inaccurate.  Also, 
since  the  authors  of  the  older  formulas  were  Europeans  or 
derived  their  data  from  European  sources,  the  maximums 
were  those  for  Europe  and  are  nat  applicable  to  this  country. 
Also  the  character  of  the  majority  of  city-street  surfaces  has 


4°  SEWERAGE. 

changed  since  that  time.  The  Kuichling,  Btirkli-Ziegler,  and 
McMath  formulas  recognize  the  variableness  in  drainage- 
surfaces. 

It  is  possible  that  a  formula  can  be  devised  which  shall 
represent  by  variable  factors  all  the  conditions  which  have 
been  shown  to  affect  the  run-off.  But  it  can  hardly  be 
expected  that  such  a  formula  can  be  other  than  cumbersome, 
and  it  is  probable  that  the  shortest  method  which  is  at  all 
rational  and  accurate  in  all  cases  is  that  of  subdividing  the 
calculation,  and  adapting  a  general  method  rather  than  a 
general  formula  to  the  peculiar  conditions  of  each  case. 
Such  a  method  is  recommended  and  will  be  outlined  further 
on. 

Many  engineers,  however,  use  some  one  of  the  formulas 
given,  and  a  large  majority  of  the  storm-sewers  built  in  this 
country  are  probably  so  designed — in  spite  of  the  fact  that 
McMath  considers  his  formula  (which  is  probably  the  most 
popular)  as  adapted  to  large  areas  only,  and  that  it  is  derived 
in  an  entirely  empirical  manner  from  St.  Louis  data  only;  and 
that  Kuichling  has  "  finally  abandoned  the  attempt  to  estab- 
lish a  general  formula  for  run-off,"  although  the  one  bearing 
his  name  is  largely  general  in  application  and  rational  in  origin 
and  construction. 

ART.  15.     EXPEDIENCY  OF  PROVIDING  FOR  EXCESSIVE 

STORMS. 

An  examination  of  rainfall  records  shows  no  apparent  law 
of  frequency  of  excessive  storms.  It  can  be  said  as  a  general 
statement,  however,  that  a  rate  of  fall  within  certain  limits 
may  be  expected  almost  any  month;  one  within  higher  limits 
five  or  more  times  in  ten  years  (these  are  the  storms  referred 
to  in  Art.  12);  and  a  phenomenal  downpour  at  most  irregular 
intervals,  usually  many  years  apart.  Should  the  sewer  be 
designed  to  carry  the  run-off  from  storms  of  the  first  class 


AMOUNT   OF  SEWAGE.  41 

only,  of  the  second  class,  or  be  of  the  greatest  size  demanded 
by  the  third  class  ? 

That  the  last  is  desirable  will  not  be  disputed,  but  both 
practical  and  financial  difficulties  frequently  oppose  this 
course.  The  practical  ones,  however,  in  most,  if  not  all,  cases 
resolve  themselves  into  financial  ones;  and  the  question 
becomes  one  of  dollars  and  cents,  and  to  a  certain  extent  also 
of  public  convenience,  which  cannot  be  assigned  a  money 
value.  To  accommodate  the  second  class  of  storms  may 
require  a  sewer  of  three  or  four  times  the  capacity  of  one 
which  would  suffice  for  the  run-off  from  the  first  class,  and 
the  third  class  a  capacity  two  or  three  times  that  of  the 
second.  The  result  of  providing  capacity  for  the  first  class 
only  would  probably  be  flooding  of  streets  and  cellars  one  or 
more  times  almost  every  year;  for  the  second  class,  flooding 
at  intervals  of  several  years;  for  the  third  class,  perfect 
immunity  from  floods. 

The  loss  resulting  from  a  flooding  of  streets  and  cellars  by 
water  more  or  less  foul  may  be  very  considerable;  goods  may 
be  damaged,  business  suspended,  foundations  weakened, 
health  threatened  by  the  dampness  lingering  after  the  floods 
have  withdrawn;  also  real-estate  values  in  a  district  liable  to 
floods  will  depreciate  and  the  city  as  a  whole  will  be  a  loser 
by  increased  tax  rates  to  meet  the  decreased  valuation.  On 
the  other  hand  as  the  capacity  of  a  sewer  increases  so  does 
the  cost,  and  this  fact  may  place  an  urgent,  even  an  impera- 
tive, limit  to  either  the  capacity  or  the  extent  of  the  sewers  to 
be  built.  The  relative  cost  of  sewers  of  different  capacities 
(other  things  supposedly  equal)  in  Washington,  D.  C.,  for 
about  10  years  is  given  in  the  following  table  (adapted  from 
one  prepared  by  Capt.  Hoxie).  The  unit  of  capacity  is  that 
of  a  12-inch  pipe. 

(  The  exact  proportion  between  the  capacity  and  the  cost, 
and  the  rule  of  their  relative  increase,  will  vary  with  different 


SEWERAGE. 
TABLE  No.  10. 


Number  of 

Relative 

-Number  of 

Relative 

Number  of 

Relative 

Units  of 

Cost 

Units  of 

Cost 

Units  of 

Cost 

Capacity. 

per  Foot. 

Capacity. 

per  Foot. 

Capacity. 

per  Foot. 

, 

I  000 

6 

1.920 

2O 

3.170 

2 

1.  174 

7 

2.OQO 

30 

3.480 

3 

1.388 

8 

2.250 

40 

4.030 

4 

1-567 

9 

2.410 

50 

4.170 

5 

1-743 

10 

2.570 

methods  of  construction,  depth  of  sewer,  etc. ;  and  in  many 
localities  the  cost  will  be  found  to  increase  more  rapidly 
relative  to  the  capacity  than  is  indicated  by  Table  No.  10. 
But  in  any  case  it  will  be  found  that  the  increase  of  cost  is 
much  less  rapid  than  that  of  capacity.  Using  the  table  of 
cost  of  Washington  sewers,  a  sewer  of  three  times  the  capacity 
of  a  12-inch  pipe  would  cost  1.388  units  of  value.  If  this 
would  just  suffice  for  the  heaviest  storms  of  the  first  class  on 
a  given  area  one  of  a  capacity  ample  for  the  maximum  of  the 
second  class,  or  four  times  as  great,  would  cost  2.8  units  of 
value,  or  about  twice  as  much;  and  one  capable  of  removing 
the  run-off  from  the  greatest  downpours,  or  twelve  times 
capacity  of  the  first,  would  cost  3.75  units  of  value,  or  only 
2.7  times  as  much  as  the  first.  Moreover,  as  we  shall  see 
later,  the  larger  mains  need  to  increase  less  rapidly  in  capacity, 
and  hence  in  cost,  to  accommodate  the  heavier  storms  than 
do  the  smaller  laterals  used  in  this  illustration. 

The  decision  as  to  which  class  of  storms  the  size  shall  be 
adapted  to  must  be  made  for  each  case  by  the  engineer  or 
the  city  authorities  as  their  judgment  dictates.  But  prob- 
ably in  nine  cases  out  of  ten  the  truest  economy  will  be 
observed  by  constructing  sewers  sufficient  for  the  second,  or 
even  in  some  cases  the  third,  class  of  storms.  The  damage 
likely  to  result  from  the  use  of  sewers  of  too  small  capacity, 
which  damage  is  to  be  balanced  against  the  extra  cost  of 
larger  ones,  will  depend  upon  circumstances.  "  If  the  sur- 


AMOUNT   OF  SEWAGE.  43 

face  flow  upon  the  streets  passes  off  to  a  proper  outlet  with- 
out causing  damage  or  inconvenience  the  flood  is  well 
disposed  of.  If  not,  there  is  danger  in  permitting  storm- 
water  to  accumulate  upon  streets  with  steep  grades.  It 
becomes  a  torrent  flowing  with  great  velocity,  and  cannot 
then  be  captured  by  inlets  designed  to  arrest,  each,  its  share 
of  shallow  gutter  flow  with  small  velocity.  It  moves  rapidly 
down  to  valleys  or  basins  without  surface  outlet;  here  it 
floods  the  surface,  because  inlets  to  receive  it  as  fast  as  it 
comes  can  rarely  be  constructed — even  should  the  drains  here 
be  of  sufficient  capacity.  Inlets  for  large  volumes  of  water 
in  city  streets  are  apt  to  be  pitfalls  for  pedestrians  and  traps 
for  cart-wheels  and  horses'  feet.  If  the  drains  of  the  inun- 
dated district  are  of  insufficient  capacity  the  consquences  are, 
of  course,  disastrous."  (Hoxie,  '*  Excessive  Rainfalls.") 

As  suggested  in  this  quotation,  it  is  possible  in  many 
localities  to  lead  the  surplus  water  of  severe  storms  over  the 
surface  to  the  nearest  natural  watercourse,  and  this  without 
any  damage  resulting,  although  it  may  be  temporarily  incon- 
venient. But  in  a  city  where  all  small  streams  have  been 
walled  in  or  diverted  to  sewers  this  is  possible  onJy  along  a 
water  front. 


CHAPTER    III. 
FLOW    IN   SEWERS. 

ART.  16.     FUNDAMENTAL  THEORIES. 

THE  flow  in  an  ordinary  sewer  must  be  due  to  one  cause 
only — the  attraction  of  gravitation.  The  velocity  of  this  flow 
is  retarded  by  friction  and  other  obstacles  affecting  it  along 
the  line  of  the  sewer. 

The  general  formula  for  the  velocity  due  to  gravity  of  a 
freely  falling  body  is  V=  V2gh,  where  V  is  velocity  in  feet 
per  second,  h  is  head  in  feet,  and  g  is  acceleration  due  to 
gravity,  being  about  32.16  feet  per  second.  In  the  case  of 
running  water  h  is  the  fall  of  the  surface  of  the  water  from 
the  point  of  no  motion  to  the  point  in  question.  Therefore 
if  there  were  no  opposing  forces  a  stream  would  flow  more 
and  more  rapidly  along  its  course  as  the  total  head  became 
greater;  and  its  velocity  would  become  constant  only  when 
the  surface  was  level,  and  therefore  h  constant.  There  is, 
however,  friction  between  the  moving  water  and  the  sides  of 
a  sewer,  and  this  must  be  overcome  by  some  force.  Since 
the  only  force  available  is  that  due  to  gravity,  called  into  play 
by  the  creation  of  a  head  h,  a  part  of  this  force  must  be  used 
in  overcoming  friction.  If  it  is  not  all  so  used  the  remainder 
goes  to  create  additional  velocity.  Friction,  it  is  found, 
increases  with  the  velocity  of  the  moving  body,  so  that,  as 
additional  increments  of  speed  are  created  by  h,  a  larger  pro- 
portion of  the  head  is  consumed  in  overcoming  friction,  until 
at  last  all  of  h  is  so  consumed  and  none  goes  to  increasing  the 

44 


FLOW  IN  SEWERS.  45 

velocity — that  is,  the  velocity  remains  constant.  Friction  also 
varies  with  the  roughness  of  the  surface.  The  total  amount 
of  energy  lost  in  friction  also  increases  with  the  duration  of  its 
action,  which  is  proportional  to  the  distance  travelled  /.  An 
important  condition  affecting  the  velocity  of  flow  in  sewers  is 
the  proportion  between  the  cross-sectional  area  of  the  stream 
and  the  length  in  this  cross-section  of  the  line  of  contact  be- 
tween the  water  and  the  bed  of  the  stream;  the  greater  the 
first  is  in  proportion  to  the  second  the  less  the  effect  of  friction 

area  of  section 

in  retarding  the  velocity.      This  proportion,  or  • — , 

wetted  perimeter 

is  customarily  represented  by  R  and  is  called  "  hydraulic  radius  " 
or  "  mean  depth." 

From  these  considerations  it  follows  that  V  varies  as  V  2gh  and 
as  some  function  of  (R),  and  inversely  as  some  function  of  (/). 
The  effect  of  roughness  may  be  represented  by  a  factor  a.  A 

formula  for  velocity  would  therefore  be  in  the  form  V  =a —  • 

In  1753  Brahms  proposed  as  a  formula  representing  the  resultant 
effect  of  these  accelerating  and  retarding  influences  V=c^RS,  in 
which  V  =•  mean  velocity  of  current,  c  is  an  empirical  constant 
which  includes  V2g  and  a,  R  is  the  hydraulic  radius,  and  5  is 

the  sine  of  the  surface  slope,  or  j.  This  formula,  now  gen- 
erally called  Chezy's  formula,  has  been  made  the  basis  of 
others,  most  of  which  differ  among  themselves  only  in  the 
values  given  to  c\  but  it  is  now  recognized  that  V  does 
not  vary  exactly  as  the  square  root  of  R  and  of  5;  that  is, 

that  f(R)  and  /(/)  in  the  formula  V=  a  ^2Shf(R}   are   not 

exactly  \i R  and  \'l\  but  they  approximate  it,  and- this 
formula  may  therefore  be  written 


4  6  SEWERAGE. 

v    ,,,.    being  equal  to  the  c  of  Chezy's  formula.      From  this 

it  follows  that  c  is  not  a  constant  for  any  particular  sewer  or 
stream,  but  varies  with  both  R  and  5.  The  principal  cause 
affecting  the  value  of  c,  however,  is  the  condition  as  to 
roughness  of  the  wetted  perimeter. 

If  we  wish  to  obtain  the  velocity  of  flow  in  any  sewer  by 
this  formula  it  is  necessary  to  select  proper  values  for  c,  R, 
and  5.  5  can  be  readily  obtained  by  dividing  h  by  /.  The 
value  of  c  and  R  and  their  relation  to  V  will  now  be  discussed. 

For  c  most  of  the  older  formulas  give  constant  values;  but 
since  V  varies  with  different  materials  of  channel-walls,  whose 
character  does  not  affect  the  values  of  R  and  5,  this  variation 
must  be  recognized  in  a  variable  c  by  means  of  a  new  factor 
or  by  a  new  equation.  Most  of  the  efforts  looking  to  greater 
accuracy  have  been  directed  toward  determining  values  for 
c  and  thousands  of  experiments  have  been  made  for  this 
purpose.  D'Arcy's  value,  somewhat  simplified  and  for  feet 
measure,  is 

__( 155256  y 

"  \i2D+  il  ' 
Bazin's  value  for  cut  stone  and  brick-work  is 

I  V 


c  = 


.0000133 


(4.354  +  -^ 


Eytelwein's  value  is  c  =  93.4. 

The  formula  evolved  from  the  records  of  a  large  number 
of  experiments  by  Messrs.  Ganguillet  and  Kutter,  usually 
called  "  Kutter's  formula,"  is  now  generally  held  to  give 
results  more  nearly  approximating  the  actual  velocities  than 
any  other.  This  formula^is,  for  English  measure, 

.00281        1.8 1 1 


c  = 


FLO W  IN  SEWERS.  47 

in  which  n  is  a  "  coefficient  of  roughness  "  of  the  sides  of  the 
channel,  such  coefficient  having  been  obtained  by  averaging 
many  experiments.  In  the  selection  of  value  for  n  great  care 
and  judgment  must  be  exercised,  particularly  for  small 
sewers,  in  the  calculation  for  which  n  has  a  greater  effect  than 
in  that  for  large  channels. 

The  values  of  n  are  approximately: 


Sides  and  bottom  of  channel  lined  with  well-planed  timber 009 

With  neat  cement,  clean  glazed  sewer-pipe,  and  very  smooth 

iron  pipe oio 

With  i  :  3  cement  mortar  or  smooth  iron  pipe on 

With  unplaned  timber  and  ordinary  iron  pipe 012 

With  smooth  brick-work  or  ordinary  pipe  sewers 013 

With  ordinary  brick-work 015 

With  rubble  or  granite-block  paving 017 


Kutter's  formula  is  seen  to  provide  for  variations  in  c  due 
not  only  to  the  character  of  the  channel  but  also  to  changes 
in  R  and  5. 

This  formula  has  been  used  to  calculate  the  tables  Nos. 
II  and  12,  n  being  taken  as  .013  in  the  former  and  .015  in 
the  latter.  If  it  is  desired  to  use  another  value  of  n  the 
corresponding  values  of  velocity  and  discharge  can  be  obtained 
very  approximately  by  multiplying  the  quantities  given  in 
each  table  by  the  factors  given  below  it  for  that  purpose. 
For  ordinary  pipe  or  good  brick  sewers  n  may  be  taken  as 
.013,  for  ordinary  brick  or  smooth  stone  as  .015.  For  extra 
smooth  work  n  may  be  taken  as  .on. 

The  uncertainties  necessarily  existing  in  the  estimates  of 
the  amount  of  sewage  to  be  provided  for  and  the  difficulty  of 
selecting  just  the  proper  value  for  n,  owing  to  the  non- 
uniform  character  of  the  interior  surface  of  the  sewer,  make  a 
refinement  of  calculations  out  of  keeping  with  the  data  used. 
Moreover,  in  the  case  of  vitrified  clay  or  concrete  pipe  the 


48 


SEWERAGE. 


TABLE  No.  11. 

VELOCITY    AND    DISCHARGE    IN    SEWERS    4    TO    36    INCHES    DIAMETER. 

Velocity  in  Feet  per  Second;  Discharge  in  Cubic  Feet  per  Minute;  Sewers  Flowing 

Full. 


(Formula  V  —  c  ^RS\  c  calculated  by  Kutte^s  formula,  with  n  =  .013.     Q  —  6oalr.) 


1  Grade  of  1 
f  Sewer.  ( 

4-inch 

6-inch 

8-inch 

io-inch 

i2-inch 

i5-inch 

i8-inch 

V 

5-75 

Q 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

.1 

30.13 

7-99 

94.10 

10.04 

210.3 

11.94 

390-8 

13.73 

647.0 

16.24 

1196.0 

18.59 

1971-5 

»5 

4.06 

21.28 

5-64 

66.48 

7.09 

148.6 

8-43 

276.1 

9.70 

457.1 

11.48 

845.0 

13.13 

1393-0 

.04 

3.63 

1903 

5-05 

59-45 

6.34 

132.9 

7-54 

246.9 

8.65 

407.8 

IO.26 

755-6 

11.74 

1244.0 

-03 

3-15 

16.47 

4.35 

51-25 

5-49 

115.0 

6-53 

213.7 

7.51 

353-9 

8.89 

654.4 

10.17 

1078.0 

02 

2-57 

13-44 

3-56 

42.00 

4.48 

93.90 

5-33 

174-5 

6.13 

289.0 

7.25 

534-2 

8.30 

880.4 

.OI 

1.82 

9-50 

2.52 

29.70 

3-17 

66.38 

3-77 

123.4 

4-33 

204.3 

5-13 

377-8 

587 

622.6 

.008 

1  .61 

8.37 

2.25 

26.53 

2.83 

59-35 

3-37 

110.3 

387 

182.6 

4-59 

337-7 

5-25 

556.8 

.006 

1.38 

7  18 

1-95 

23.00 

2-45 

51.39 

2.92 

95-55 

3.35 

158  2 

3-97 

292.5 

4.55 

482.3 

.004 

1-59 

18.71 

2.00 

41.85 

2.38 

77-98 

2-74 

I29.I 

3-24 

238.3 

3  70 

392.9 

.002 

I.40 

29.38 

1.67 

546i 

1.91 

90.40 

2.27 

167.3 

2.60 

275.9 

.OOI 

1.17 

38.41 

1-35 

63.58 

i.  60 

117.7 

1.83 

194-3 

OOOQ 

1.51 

in.  4 

1-73 

183.9 

0008 

1.63 

i73.i 

OOO7 

1.52 

161.2 

For  n  =  .on        .012        .013        .015        .017 
Multiply  V  or  Q  by  1.20         1.09         i.oo        0.84        0.73 

i  gallon  per  day  —  .00009284  cubic  feet  per  minute. 
I  cubic  foot  per  minute  —  10,771  gallons  per  day. 


FLOW  IN  SEWERS. 


49 


TABLE  No.  11. — Continued. 

VELOCITY    AND    DISCHARGE    IN    SEWERS    4    TO    36    INCHES  DIAMETER. 

Velocity  in  Feet  per  Second  ;    Discharge  in  Cubic  Feet  per  Minute  ,    Sewers 

Flowing  Full. 

(Formula  V  =  c  \' 'RS  ;   c  calculated  by  Kutter's  formula,  with  n  =  .013.     Q  =  6oaV.) 


Grade  of 
Sewer. 

ao-inch 

•22-inch 

a^inch 

30-  inch 

33-inch 

36-inch 

y 

g 

V 

Q 

V 

Q 

4319 

y 

Q 

V 

Q 

V 

Q 

.1 

20.08 

2628 

21.51 

3407 

22.91 

26.84 

7905 

28.69 

IO22O 

30.46 

12920 

•05 

14.18 

1857 

15.20 

2407 

16.  19 

3052 

18.97 

5586 

20.27 

7225 

21-54 

9136 

.04 

12.69 

1661 

13-59 

2153 

14-47 

2729 

16.96 

4995 

18.13 

6461 

19.26 

8171 

.03 

10.98 

1438 

11.77 

1864 

12.53 

2363 

14.69 

4325 

fS-70 

5595 

16.68 

7075 

.02 

8.97 

1174 

9.61 

1522 

10.23 

1930 

11.99 

3532 

12.82 

4568 

13.62 

5777 

.01 

e.34 

830 

6.79 

1076 

7.24 

1366 

8.48 

2497 

9.06 

3230 

9.63 

4085 

.008 

5.67 

742 

6.07 

962 

6.47 

1210 

7-58 

2233 

8.  ii 

2889 

8.61 

3653 

.OO6 

4.91 

643 

5.26 

833 

5-6o 

1057 

6.57 

1934 

7.02 

2502 

7.46 

3164 

.004 

4.00 

524 

4.29 

679 

4.56 

860 

5-35 

1576 

5.72 

2040 

6.08 

2580 

.002 

2.81 

368 

3.01 

477 

3-21 

605 

3.76 

1109 

4.02 

1434 

4.28 

1814 

,001 

1.98 

259 

2.12 

336 

2.26 

427 

2.66 

782 

2.84 

1012 

3.02 

1281 

.0009 

1.87 

245 

2.01 

3i8 

2.14 

404 

2.51 

74i 

2.69 

959 

2.86 

1213 

.0008 

1.76 

231 

1.89 

299 

2.02 

380 

2.37 

697 

2-53 

902 

2.69 

1141 

.0007 

1.64 

215 

I.76 

279 

1.88 

354 

2.20 

650 

2.36 

841 

2.51 

1065 

.0006 

I-5I 

198 

1.63 

258 

1-73 

327 

2.04 

600 

2.18 

777 

2.32 

984 

.OOO5 

I.48 

234 

1.58 

298 

1.86 

546 

1.99 

708 

2.  II 

896 

.0004 

1.32 

208 

1.40 

265 

1.65 

486 

1.77 

630 

1.88 

798 

.0003 

1.20 

227 

1.40 

413 

1-52 

54i 

1.62 

686 

.OOO2 

0.98 

186 

1.  13 

335 

1.22 

435 

1.30 

552 

SEWERAGE. 


TABLE    No.    12. 


VELOCITY    AND    DISCHARGE    IN    SEWERS    33    INCHES    TO    IO    FEET 

DIAMETER. 

Velocity  in  Feet  per  Second;  Discharge  in  Cubic  Feet  per  Minute;  Sewers 

Flowing  Full. 

(Formula  V  •=  c  ty ' RS  ;  c  calculated  by  Kutter's  formula,  with  n  =  .015.     Q  = 


Grade  of 
Sewer. 

33-inch 

36-inch 

42-inch 

4  -foot 

V 

Q 

V 

Q 

V 

Q 

y 

Q 

•05 

17.17 

6120 

18.27 

7750 

20.37 

11765 

22.36 

16865 

.04 

15.36 

5473 

16.34 

6930 

18.21 

10517 

20.00 

15080 

•03 

I3-30 

4738 

14.15 

6000 

15.77 

9108 

17.31 

13057 

.02 

10.85 

3868 

ii-55 

4900 

12.88 

7437 

14-13 

10658 

.01 

7.68 

2735 

8.16 

3464 

9.09 

5258 

9-99 

7537 

.008 

6.86 

2444 

7-30 

3096 

8.14 

4700 

8-93 

6738 

.006 

5-94 

2115 

6.32 

2679 

7.04 

4067 

7-73 

5832 

.004 

4.84 

1726 

5.15 

2186 

5-75 

3243 

6.31 

4759 

.002 

3-41 

1216 

3.63 

1540 

4-05 

2339 

4-45 

3354 

.OOI 

2.40 

856 

2.55 

1085 

2.85 

1648 

3-13 

2365 

.0009 

2.27 

810 

2.42 

1027 

2.70 

1561 

2.97 

2240 

.0008 

2.14 

763 

2.28 

967 

2-55 

1470 

2.80 

2110 

.OOO7 

2.OO 

713 

2.13 

9<>3 

2.38 

1373 

2.61 

1972 

.0006 

1.85 

658 

1.97 

834 

2.  2O 

1269 

2.42 

1822 

.0005 

1.68 

598 

1.79 

759 

2.OO 

"55 

2.  2O 

I658 

.OOO4 

1.49 

532 

1-59 

675 

1-78 

1028 

1.96 

1477 

.0003 

1.28 

457 

1-37 

580 

1-53 

883 

1.68 

I27O 

..0002 

1.23 

712 

1.36 

1026 

.00015 

1.16 

878 

For  n  —  .on       .012 
Multiply  V  or  Q  by  1.43      1.29 


.013      .015       .017 
1.19      i. oo      0.87 


FLOW  IN   SEWERS. 


TABLE    No    12. — Continued. 

VELOCITY    AND    DISCHARGE    IN    SEWERS    33    INCHES    TO     IO    FEET 

DIAMETER. 
Velocity  in  Feet  per  Second;  Discharge  in  Cubic  Feet  per  Minute;  Sewers 

Flowing  Full. 
(Formula  V  =  c  \/~RS ';  c  calculated  by  Kutter's  formula,  with  n  =  .015.     Q  = 


Grade  of 
Sewer. 

S-foot 

6-foot 

8-foot 

io-foot 

V 

Q 

V 

Q 

V 

Q  - 

V 

Q 

.05 

26.05 

30700 

.04 

23.30 

27450 

26.34 

44690 

•03 

20.17 

23765 

22.  8l 

38700 

.02 

16.47 

19405 

18.62 

31600 

22.53 

67965 

26.03 

122700 

.01 

11.64 

I37I7 

13-  -17 

22345 

15-93 

48050 

18.41 

86755 

.008 

10.41 

12267 

11.78 

19980 

14.25 

42970 

16.46 

7759° 

.006 

9.01 

10617 

10.19 

17295 

12-33 

37200 

14.25 

67175 

.004 

7.36 

8665 

8.32 

I4H3 

10.07 

30370 

11.63 

54840 

.OO2 

5.19 

6110 

5.87 

9956 

7.10 

21435 

8.21 

37600 

.001 

3.66 

43ii 

4.14 

7030 

5  -O2 

15150 

5-81 

27380 

.0009 

3-47 

4083 

3.92 

6659 

4.76 

14353 

5.51 

25960 

.0008 

3-27 

3849 

3-70 

6276 

4.49 

13533 

5-19 

24475 

.0007 

3-05 

3597 

3.46 

5870 

4.20 

12660 

4.86 

22895 

.0006 

2.82 

3326 

3-20 

5429 

3.88 

11710 

4-50 

21195 

.0005 

2-57 

3028 

2.92 

4946 

3.54 

10675 

4.10 

19325 

.0004 

2.29 

2700 

2.60 

4411 

3.16 

9532 

3-66 

17267 

.0003 

1.97 

2324 

2.24 

3801 

2.73 

8228 

3-17 

14927 

.0002 

i.  60 

1882 

1.82 

3083 

2.22 

6694 

2.58 

12168 

.00015 

i-37 

1615 

1.56 

2650 

I.QI 

5760 

2.23 

10510 

.OOOI2 

1.39 

2353 

1.70 

5137 

1.99 

9375 

.00010 

1-55 

4672 

1.81 

8542 

.000095 

1.25 

3783 

i-77 

8320 

.000090 

1.72 

8096 

52  SEWERAGE. 

market  sizes  must  in  the  end  be  those  selected,  and  there  is 
a  considerable  jump  between  the  capacities  of  consecutive 
sizes.  For  instance,  an  8-inch  pipe  on  a  \%  grade  will  dis- 
charge about  498  gallons  per  minute  when  running  full;  a 
lo-inch  pipe  running  full  with  the  same  grade  will  discharge 
about  925  gallons  per  minute,  and  a  12-inch  pipe  about  1530 
gallons  per  minute.  For  this  reason  it  is  sufficiently  accurate 
and  often  more  convenient  to  use  curves  plotted  from  the 
tables,  having  the  grade  and  corresponding  velocity  or  dis- 
charge as  coordinates,  from  which  the  flow  through  any  cus- 
tomary size  of  sewer  at  any  practicable  grade  can  be  found  at 
a  glance  and  with  as  great  accuracy  as  is  required  for  ordinary 
use.  Such  a  diagram  can  be  readily  prepared  on  a  sheet  of 
cross-section  paper,  a  curve  being  drawn  for  the  velocity  and 
another  for  the  discharge  of  each  size  of  sewer. 

It  is  now  generally  considered  that  Kutter's  formula  gives 
somewhat  too  small  values  for  sewers  under  15  or  18  inches 
diameter. 

It  must  be  remembered  that  the  formulas  and  tables  of 
velocity  are  supposed  to  apply  only  when  the  sewage  has 
reached  a  constant  velocity.  Previous  to  this  when  the  fric- 
tion does  not  consume  all  of  h  the  remainder  is  creating 
increments  of  velocity.  Since  the  same  amount  of  sewage 
must  pass  all  sections  of  a  sewer  between  two  inlets,  however, 
it  follows  that,  previous  to  the  flow  obtaining  its  maximum 
and  constant  velocity,  the  depth  of  sewage  must  have  been 
greater,  increasing  up  stream  to  the  point  of  entry.  An 
initial  velocity  of  entrance  in  the  direction  of  the  sewage  flow 
will  reduce  the  amount  and  extent  of  this  non-uniform  flow 
with  larger  cross-section,  but  will  have  little  effect  upon  the 
ultimate  constant  velocity.  If  no  such  initial  velocity  exist 
the  entering  sewage  must,  if  it  be  any  large  percentage  of  the 
capacity  of  the  sewer,  back  up  the  feeding-pipe  through  which 
it  entered  in  order  to  create  additional  head  h. 


FLOW  IN  SEWERS. 


53 


V  is  the  mean  velocity.  The  effect  of  friction  is  exerted 
along  the  wetted  perimeter  and  grows  less  toward  the  centre 
of  the  stream.  The  surface  of  flow  is  also  retarded  by  friction 
with  the  air,  and  frequently  in  the  case  of  house-sewage  by 
a  greasy  scum  which  floats  upon  the  surface.  The  velocity 
given  is  really  the  volume  of  flow  divided  by  its  area. 


Since  V  varies  as 


/(*)=/(; 


area 


\ 


it  follows 


^wetted  perimeter/' 
that  the  size  of  the  sewer  and  the  shape  of  the  cross-section 
have  considerable  effect  upon  the  velocity  of  a  stream.     The 

area 


maximum    value    of 


for   a    sewer  flowing  full    is 


perimeter 

obtained,  we  learn  from  geometry,  by  making  the  cross- 
section  circular;  that  is,  for  pipes  of  the  same  area,  but  differ- 
ent shapes  of  cross-section,  flowing  full,  the  circular  gives  the 
largest  R.  But  this  is  not  generally  true  when  the  sewer  is 
not  flowing  full. 

If  we  examine  the  effect  of  depth  of  flow  in  a  given  cir- 
cular sewer  upon  the  value  of  R  we  find  that  if  the  depth 

d  =  —  (D  equalling  the  diameter  of  the  sewer)  a  =  .3927/2% 

/  —  i. 5 708 A  and  R  =  0.25/7.  If  the  depth  =  D  we  find 
a  —  0.7854/7,  /  =  3. 1416/2,  and  R  =  0.25/7  as  before. 

TABLE  No.  13. 


p 

a 

R 

By  Kutter's  Formula. 

d 
Depth. 

Wetted 
Perimeter. 

Area  of 
Flow. 

Hydraulic 
Radius. 

a  VI 

Corrected  Propor- 

Corrected Propor- 

tional Velocities. 

tional  Discharge. 

Full,  i.o 

3-142 

0.7854 

0.250 

.00 

.00 

1.000 

0-95 

2.691 

0.7708 

0.286 

.07 

.11 

I  ,068 

0.9 

2.498 

0-7445 

0.298 

.09 

•15 

J-073 

0.8 

2.214 

0.6735 

0.304 

.IO 

.16 

0.98 

0.7 

.983 

0.5874 

0.296 

.08 

.14 

0.84 

0.6 

.772 

0.4920 

0.278 

05 

.08 

0.67 

~-o-S 

•571 

0.3927 

0.250 

1.  00 

.00    —- 

0.50 

0.4 

.369 

0.2934 

0.214 

0.93 

b.88 

0-33 

0-3 

•159 

o.  1981 

0.171 

0.83 

0.72 

0.19 

0.25 

.047 

0.1536 

0.146 

0.76 

0.65 

0.14 

0.2 

0.927 

0.1118 

O.I2I 

0.69 

0.56 

0.09 

O.I 

0.643 

0.0408 

0.0635 

0.50 

0.36 

0.03 

54 


SEWERAGE. 


As  the  depth  of  the  sewage  decreases  from  that  of  half  the 
diameter  the  area  decreases  more  rapidly  than  does  the 
wetted  perimeter,  and  consequently  R  decreases  more  and 
more  rapidly  as  the  depth  diminishes.  The  above  table 
shows  this  very  plainly.  The  diameter  is  here  taken  as  unity  ? 
the  sewer  circular. 

The  formula  for  R  for  circular  sewers  for  any  given  depth 
of  flow  is 


area 


~       sn  a  COS  a 


wetted  perimeter 


1 80  sin  a  cos 


2a 
360 


X 


in  which  r  =  the  radius  of  the  sewer  perimeter; 

a  =  the  number  of  degrees  in  the  angle  whose  cosine 

r  —  the  depth  of  flow 

is -. 

r 

For  the  egg-shaped  sewer  (see  Art.  24)  somewhat  different 
values  are  found. 

TABLE  No.   14. 

EGG-SHAPED    SEWER. 
(D  =  horizontal  diameter  ;  H  =  vertical  diameter.) 


By  Kutter's  Formula. 

d 

d 

in  parts 
oiH. 

d 
in  parts 
of  D. 

P 

in  parts 
of  D. 

a 
in  parts 
of/?*. 

R 
in  parts 
of  D. 

i.8587|/* 

Corrected 
Propor- 
tional 

Corrected 
Propor- 
tional 

in  Circular 
Sewer 
in  parts  of 

7"J  * 

Velocities.  Discharge. 

u.* 

Full  1.  000 

1.50 

3.965 

1.1485 

0.2897 

1.  000 

1.  00 

I.OO 

1.209 

0.667 

1.  00 

2-394 

0.7558 

0.3157 

1.045 

1.  06 

0.69 

0.750 

0.333 

0.50 

I  374 

0.2840 

0.2066 

0.846 

0.77 

o.i  8 

0.354 

0.267 

0.40 

1.  159 

0.20485 

0.  1  768 

0.781 

0.70 

0.  12 

0.284 

O.22O 

0-33 

I.OI2 

O.I55IO 

0.1532 

0.727 

0.63 

O.oSl 

0.228 

0.200 

0.30 

0-937 

0.13471 

0.1437 

0.704 

0.60 

0.064 

0.214 

0.133 

O.2O 

0.706 

0.07497 

O.K>62 

0.606 

0-49 

0.030 

0.141 

0.067 

0.10 

0.463 

0.0279 

O.O6O26 

0-455 

0.33 

O.OO8 

0.075 

0.033 

0.05 

0.321 

0.0102 

0.03177 

0.331 

0.23 

O.OO2 

0.039 

*To  give  equal  discharge  in  circular  sewer  of  same  capacity — i.e.,  one  whose  diameter 


FLOW  IN  SEWERS.  55 

By  Table  No.  13  it  is  seen  that  when  a  circular  sewer  is 
half  full  the  wetted  perimeter  and  area  of  flow  are  each  half 
of  that  for  a  full  sewer.  When  the  depth  is  but  J  the 
diameter,  however,  the  wetted  perimeter  is  -J,  the  area  of  flow 
less  than  £,  and  R  about  %  that  of  a  full  sewer;  and  when  the 
depth  is  y^  the  wetted  perimeter  is  about  £,  the  area  y1^,  and 
R  about  J  that  of  a  full  sewer. 

In  the  last  two  columns  we  have  the  proportional  veloci- 
ties and  discharges  for  various  depths  of  flow,  with  allowance 
made  for  variations  in  cy  calculated  by  Kutter's  formula,  with 
sufficient  accuracy  for  ordinary  use.  The  fifth  column  shows 
proportional  velocities  if  c  is  considered  as  not  affected  by 
changes  in  R.  A  comparison  of  the  fifth  and  sixth  columns 
shows  the  effect  upon  the  coefficient  c  of  variations  in  R, 
since  if  c  =  x  for  a  full  sewer  for  one  .2  full  it  equals  $-|;tr 
and  for  one  .8  full  \\^x. 

Reference  to  Table  No.  13  shows  that  if,  in  a  circular 
sewer  with  a  depth  of  flow  of  J  the  diameter,  the  velocity  is 
i \  feet  per  second  (the  minimum  velocity  of  flow  ordinarily 
permissible  for  house-sewers),  in  the  same  sewer  flowing  full 
the  velocity  will  be  2.3  feet  per  second.  It  also  appears  from 
this  table  that  the  greatest  velocity  is  attained,  not  when  the 
sewer  is  flowing  full,  but  when  the  depth  is  .81  of  the  diam- 
eter, and  that  the  maximum  discharge  occurs  when  the  depth 
is  .9  of  the  diameter.  From  this  it  follows  that  a  circular 
sewer  can  never  flow  full  unless  under  a  head. 

The  tables  Nos.  11  and  12  for  flow  in  sewers  give  the 
velocity  and  discharge  for  full  sewers  only,  the  velocity  being 
the  same  for  a  sewer  half  full,  while  the  discharge  is  one  half 
as  great.  They  do  not  give  the  maximum  capacity  of  the 
sewer,  which  is  theoretically  1.07  times  that  given;  but  the 
velocity  and  discharge  for  sewers  flowing  full  are  most  con- 
venient for  use  and  are  on  the  safe  side  of  exact  accuracy. 

Where  it  is  desired  to  obtain  the  velocity  or  discharge  of 


56  SEWERAGE. 

a  sewer  flowing  partly  full  the  tables  can  be  entered  with  the 
quantities  corresponding  to  the  other  conditions,  the  velocity 
or  discharge  of  the  sewer  as  if  it  were  flowing  full  obtained, 
and  such  part  of  this  taken  as  is  indicated  by  the  above  table 
for  the  given  depth.  For  instance,  if  it  is  desired  to  find  the 
discharge  of  a  lO-inch  circular  sewer,  grade  I  :  200,  when  the 
depth  of  flow  is  0.4  the  diameter,  we  find  from  the  table  that 
the  discharge  if  running  full  would  be  about  650  gallons  per 
minute;  we  multiply  this  by  0.33  and  obtain  214  gallons,  the 
volume  required.  Or,  given  the  volume,  215  gallons,  and  the 
grade,  I  :  200,  to  find  the  depth  of  flow:  we  find  the  flow  of 
a  full  sewer,  650  gallons,  divide  215  gallons  by  this,  obtaining 
•J,  and  find  the  depth  corresponding  to  this  proportion  of  the 
discharge,  or  0.4. 

The  velocity  obtained  by  the  formula  or  from  the  table 
is  that  for  a  straight  pipe  of  a  uniform  cross-section  and 
condition  of  surface.  In  a  system  of  sewers  there  are 
numerous  curves,  irregularities  of  surface,  manholes,  house- 
branches,  etc.,  each  of  which  may  exert  a  retarding  in- 
fluence upon  the  sewage.  It  is  thought  that  there  is  no  ap- 
preciable diminution  of  velocities  in  a  curve  whose  radius  is  at 
least  5  times  the  diameter  of  the  sewer.  Weisbach's  formula 
for  loss  of  head  in  curves  is 


in  which  c  =  .131  +  1.847 

r  =  radius  of  pipe; 

b=       w      "    bend; 

a  =  angle  in  degrees; 

K=  velocity  in  feet  per  second; 

h  =  head  in  feet  necessary  to  overcome  resistance  of 

curve. 
From  the  above  formula  we  find  that  if 


FLO  W  IN  SEWERS.  57 

£=     .1          .2         .3         .4        -5         -6         .7         .8  .9         1.0 

then 

c  =  .i$i    .138    .158    .206   .294  .440  .661    .977   1.408    1.978 

As  an  example,  assume  a  lO-inch  pipe,  or  r  =  0.42  feet, 
that  b  =  2  feet,  that  a  =  90°,  that  V  —  3  feet.  Then  h  = 

'          — ^— —  .0097  feet,  or  less  than  %  inch.     This  result 

is  not  sufficiently  large  to  materially  affect  the  design.  It 
represents  the  case  of  a  junction  between  sewers  made  by  a 
curve  in  a  manhole  (see  Plate  VIII,  Fig.  5).  This  formula, 
however,  does  not  apply  to  the  foaming  or  impact  created  by 
an  angle.  A  very  considerable  loss  of  head  may  result  from 
this,  and  consequently  sharp  bends  should  be  avoided  unless 
it  is  desired  to  reduce  the  velocity. 

The  obstructions  to  flow  offered  by  manholes,  house-con- 
nections, etc.,  can  be  almost  entirely  avoided  by  careful 
designing  and  construction.  That  due  to  roughness  of  the 
material  of  construction  should  also  be  kept  low,  but  will 
necessarily  be  considerable.  This  obstruction  should  be 
allowed  for  in  the  formula  by  modifying  the  value  of  c  through 
the  different  values  of  n. 

ART.   17.     LIMITS  OF  VELOCITY. 

The  formula  for  the  quantity  of  sewage  which  will  flow 
through  a  given  sewer  per  second  is  Q  =  Va,  in  which  a  is  the 
area  of  the  stream  flowing.  It  would  appear  that,  given  Qt 
Fand  a  could  take  any  value  so  long  as  Va  =  Q.  a  is,  how- 
ever, limited  in  its  maximum  by  economic  considerations,  also 
sometimes  by  practical  ones  (see  Art.  23).  Falso,  although, 
if  pure  water  were  the  material  flowing  through  the  sewers,  it 
might  vary  from  o  to  infinity,  is  limited  within  a  compara- 
tively narrow  range  by  the  character  of  ordinary  sewage. 

House-sewage    contains    some   matter    which    is    slightly 


58  SEWERAGE. 

heavier  than  water,  also  much  which  is  lighter;  the  former 
tends  to  settle  in  the  bottom  of  a  sewer,  the  latter  to  collect 
along  the  edges  of  the  stream.  Ashes,  garbage,  clothing,  and 
other  refuse  matter  should  be  kept  out  of  the  sewers  by  laws 
rigidly  enforced,  but  in  spite  of  all  precautions  such  material 
will  at  times  reach  them.  Dirt  and  sand  frequently  enter 
house-sewers  through  the  ventilation-holes  in  manhole-heads 
or  through  defective  joints  in  the  sewer.  As  no  system  is 
perfect  or  perfectly  managed,  provision  should  be  made  for  a 
certain  amount  of  such  matter.  It  is  found  that  if  the 
velocity  of  a  stream  be  sufficiently  great,  matter  suspended  in 
the  water  will  not  be  deposited,  but  a  retarding  of  the  velocity 
at  any  point  may  cause  a  formation  of  deposits  there.  Ex- 
periments have  been  made  to  determine  the  velocities  neces- 
sary for  flowing  water  to  render  it  capable  of  transporting 
matter  of  various  sizes  and  densities,  though  usually  earth, 
sand,  gravel,  and  stones  have  been  used.  The  results 
obtained  by  DuBuat  are  those  usually  quoted,  and  are  given 
as  being  approximately  correct  for  channels  of  uniform  cross- 
section.  The  velocities  are  those  sufficient  to  move  the  par- 
ticles along  the  bottom  of  the  channel  and  are  in  feet  per 

second. 

TABLE  No.  15. 

MATERIALS    MOVED    BY  WATER  FLOWING    AT    DIFFERENT  VELOCITIES. 
Material.                                          Bottom  Velocity.  Mean  Velocity. 

Pottery-clay 0.3  0.4 

Sand,  size  of  anise-seed 0.4  0.5 

Gravel,  size  of  peas 0.6  0.8 

"          "     "   beans 1.2  1.6 

Shingle,  about  i  inch  in  diameter 2.5  3.3 

Angular  stones,  about  \\  inches  in  diameter 3.5  4.5 

Other  experiments  have  given  slight  variations  from  these 
figures,  but  they  are  sufficiently  accurate  for  ordinary  use. 
It  must  be  remembered  that  they  apply  to  loose  material  only. 
Where  clay  or  sand  has  formed  a  compact  deposit  in  a  sewer 
many  times  these  velocities  may  be  required  to  move  it. 
Just  which  of  these  or  similar  materials  the  sewage  should  be 


FLOW  IN  SEWERS.  59 

given  sufficient  velocity  to  hold  suspended  is  a  question. 
But  it  has  been  found  in  practice  that  an  actual  velocity  of  i£ 
feet  per  second  will  ordinarily  suffice  to  prevent  deposits 
where  house-sewage  alone  is  admitted. 

Where  storm-water  from  the  streets  is  admitted  to  the 
sewers  clay,  sand,  gravel,  leaves,  etc.,  as  well  as  lighter  matter 
are  washed  through  the  inlets.  The  velocities  in  these  sewers 
should  be  sufficient  to  prevent  the  deposit  of  such  material, 
which  velocity,  according  to  the  table  given  above,  would 
needs  be  about  3.5  feet  per  second. 

The  velocity  given  for  house-sewers — \\  feet  per  second 
— is  that  which  should  be  maintained  as  a  minimum  by  the 
ordinary  minimum  daily  flow;  that  for  storm-sewers — 3.5  feet 
per  second — is  the  least  which  should  be  attained  in  time  of 
storms. 

The  average  daily  flow  in  house-sewers  may  be  taken 
(Art.  14)  as  ^  of  the  maximum  to  be  provided  for,  and  the 
ordinary  minimum  as  \  of  this.  At  night-time,  when  the 
absolute  minimum  usually  occurs,  the  sewage  is  composed  of 
comparatively  pure  water  and  a  lessened  velocity  due  to  a 
shallower  flow  will  not  be  particularly  detrimental,  f  of  the 
maximum  volume  for  which  the  sewer  is  designed  may  there- 
fore be  assumed  as  that  for  which  the  velocity  should  be 
i£  feet  per  second.  For  reasons  to  be  given  (Art.  23)  a  house- 
sewer  is  usually  designed  to  be  50$  to  ioo#  larger  than 
required  by  the  assumed  volume  of  sewage,  so  that  the  ordi- 
nary minimum  can  be  taken  as  being  \  to  %  of  the  capacity  of 
the  sewer.  Reference  to  Table  No.  13  shows  that  this 
quantity  is  carried  w'len  the  depth  of  flow  in  the  sewer  is  .25 
to  .3  the  diameter  and  when  the  velocity  is  .65  to  .72  that 
for  a  sewer  flowing  full.  It  follows  from  this  that  the  grade 
of  a  house-sewer  should  be  such  that  the  velocity  when  flow* 

ing  full  is  at  least  -^—  to  ~^—t  or  2.3  to  2. 1  feet  per  second. 
.05        .72 


6o  SEWERAGE. 

In  the  case  of  storm-sewers,  which  carry  no  house-sewage 
and  are  thus  dry  for  a  large  portion  of  the  time,  it  may  be 
assumed  that  in  general  any  storm  which  will  wash  any  con- 
siderable amount  of  gravel  and  dirt  into  them  will  require  at 
least  one  third  of  the  capacity  of  the  sewer.  Such  grades 
should  therefore  be  given  these  as  will  cause  a  velocity  of  at 
least  3.5  feet  per  second  when  the  sewer  is  flowing  one 
third  full,  or  4  feet  when  flowing  full.  Smaller  showers, 
which  will  give  less  depth  of  water  in  the  sewer,  it  may 
likewise  be  assumed  will  contribute  only  such  matter  as  is 
transported  by  less  velocities. 

It  may  in  some  cases  be  necessary  to  construct  sewers 
giving  somewhat  lower  velocities  than  these,  but  this  should 
be  only  after  careful  consideration  of  the  problem.  House- 
sewers  should  never  be  designed  with  grades  giving  a  less 
velocity  than  2  feet  per  second  when  flowing  full,  nor  storm- 
sewers  with  those  giving  less  than  3  feet. 

Where  a  combined  sewer  is  in  question — i.e.,  one  which 
daily  carries  house-sewage,  but  which  also  has  sufficient 
capacity  for  and  acts  as  a  storm-sewer — the  requisite  velocity 
must  be  obtained  for  both  house-  and  storm-sewage.  But 
except  in  very  unusual  instances  a  grade  which  will  meet  the 
requirements  of  house-sewage  will  more  than  satisfy  the 
demands  of  storm-water  transportation.  For,  since  the  maxi- 
mum amount  of  house-sewage  per  second  per  acre  in  a  resi- 

80  x  175 

dence  district  will  be  about 5 —  — 0-^ =  .022  cubic  feet, 

7.48    X    86400 

while  the  storm-water  from  such  an  area  may  be  3  cubic  feet 
per  second,  or  140  times  as  great,  if  a  circular  sewer  is 
designed  to  give  a  velocity  of  I J  feet  when  it  is  carrying  .007 
of  its  full  capacity  its  velocity  when  flowing  full  will  be  about 
9  feet,  or  more  than  twice  the  desired  velocity;  while  with  an 
egg-shaped  sewer  under  the  same  conditions  a  velocity  of  4.7 
feet  when  flowing  full  is  obtained. 


FLO W  IN  SEWERS.  61 

The  subject  of  maximum  velocities  has  received  but  little 
attention,  probably  because  the  dangers  connected  with 
excessive  velocities  are  not  so  great  as  those  resulting  from  a 
too  slow  rate.  Such  dangers  do  exist,  however.  The  more 
immediate  one  is  that  the  consequent  shallowness  of  the 
current  which  would  in  many  cases  result  would  occasion  the 
deposit  of  the  larger  floating  solids,  which  may  result  in 
obstinate  obstructions  in  the  sewer.  In  the  mains  this  can  be 
obviated  by  reducing  the  size  of  the  sewer  to  the  point  where 
the  necessary  depth  is  obtained.  But  it  is  usually  not  in  the 
mains  but  in  the  branches  that  steep  grades  are  possible.  To 
reduce  the  sewer  to  such  a  size  as  would  give  any  consider- 
able depth  to  the  daily  flow  on  very  steep  grades  would  call 
for  a  diameter  much  below  that  usually  adopted  as  a  mini- 
mum. An  8-inch  sewer  whose  grade  is  o.  I  gives  a  theoretic 
velocity  of  10.04  feet  per  second  when  flowing  full.  To 
secure  a  flow  in  this  pipe  having  an  average  depth  of  4  inches 
would  require  the  sewage  from  a  population  of  6500.  In 
general  it  may  be  said  that  the  ordinary  depth  of  flow  in  any 
sewer  should  not  be  less  than  2  inches,  nor  should  it  be 
less  than  \  the  radius  of  the  invert,  since  if  it  is  so  there 
is  much  more  danger  of  deposits  forming  along  the  edges 
and  even  in  the  centre  of  the  stream.  It  will  sometimes  be 
impossible  to  meet  this  requirement  fully,  but  it  should  be 
kept  in  mind  as  extremely  desirable. 

Another  objection  to  too  great  velocity  is  the  danger  of 
attrition  of  the  sewer-invert  by  the  scouring  action  of  sand, 
stones,  etc.,  swept  rapidly  over  it.  In  brick  sewers  this 
objection  is  frequently  and  successfully  met  by  lining  the 
invert  with  granite  blocks.  A  5^-foot  two-ring  brick  sewer 
in  Baltimore,  25  years  old,  has  been  found  with  its  invert 
in  one  place  cut  completely  through  for  a  width  of  12  to  15 
inches  and  badly  worn  for  a  height  of  2  feet,  and  many  other 
places  were  only  a  little  less  damaged.  In  Omaha's  brick 


62  SEWERAGE. 

sewers  the  wear,  which  is  usually  18  to  24  inches  wide, 
became  2  to  3  inches  deep  in  12  years.  In  both  cities  ordi- 
nary brick  was  used,  but  was  replaced  with  stone  blocks. 

The  first  objection  is  the  serious  one,  since  the  time  taken 
to  wear  out  a  sewer-invert  must  be  considerable  if  good 
material  is  used,  and  replacing  it  is  a  matter  of  expense  only. 
But  the  forming  of  deposits  in  the  sewer  endangers  the  health 
of  the  community. 

It  is  difficult  to  set  a  maximum  limit  to  the  velocity  allow- 
able, but  it  may  generally  be  taken  as  from  8  to  12  feet  per 
second.  From  3  to  5  feet  per  second  is  probably  the  most 
desirable  velocity. 

ART.  18.     SIZE  OF  SEWERS. 

If  a  house-sewer  were  constructed  to  exactly  meet  the 
theoretical  requirements  as  above  outlined  it  would  contin- 
ually increase  in  size  from  the  head  to  the  outlet,  by  a  small 
increment  below  each  house-connection,  by  a  larger  one  below 
each  tributary  branch  or  lateral;  but  between  the  first  two 
connections  it  should  be  of  sufficient  size  to  carry  the  sewage 

of  one  house  only,    which   would   be   about ~ 

7.48   X   86400 

=  .0016  cubic  feet  per  second,  which  at  a  velocity  of  2.5  feet 
per  second  would  call  for  a  pipe  of  .00064  square  feet  area, 
or  \  inch  diameter. 

This  method  is  not  closely  followed  for  the  reasons  that 
the  data  on  which  are  based  the  calculations  of  volume  of 
sewage  as  well  as  the  formulas  of  flow  cannot  be  exact  enough 
to  warrant  it;  that  the  estimate  of  ultimate  population  may 
be  exceeded;  that  the  per  capita  water-consumption  may 
increase  beyond  the  maximum  assumed,  factories  or  other 
large  contributors  of  sewage  locate  at  points  where  they  were 
not  expected,  or  for  some  other  cause  the  amount  of  sewage 


FLOW  IN  SEWERS.  63 

reaching  any  lateral  may  be  largely  exceeded.  This  excess 
can  be  allowed  for  in  a  general  way  only,  but  it  is  advisable  to 
design  the  laterals  of  a  capacity  double  that  calculated,  par- 
ticularly since  the  cost  is  not  thereby  largely  increased,  and 
the  velocity  in  a  sewer  flowing  half  full  is  as  great  as  that  in 
one  flowing  full. 

The  house-sewer  mains  need  not  have  so  great  an  excess 
of  size,  since  they  carry  the  sewage  from  many  laterals,  and 
it  is  not  probable  that  all  these  will  receive  double  the  calcu- 
lated amounts  of  sewage.  It  will  probably  be  sufficient  to 
increase  these  by  50$  of  the  estimated  capacity.  The  volume 
of  sewage  reaching  the  trunk  or  outlet  sewer  can  be  still  more 
closely  calculated,  and  an  increase  of  25$  may  be  made  as 
giving  it  sufficient  capacity,  although  it  would  probably  be 
better  to  add  50$  here  also,  the  additional  cost  being  slight  in 
most  cases. 

With  this  increase  the  head  of  each  lateral  would  still  be 
less  than  \  inch  in  diameter.  This  would  be  too  small  to 
adopt  in  practice  for  several  reasons:  because  an  individual 
house  will  contribute  sewage  at  occasional  maximum  rates  far 
exceeding  175$  of  their  daily  average;  because  a  very  small 
sewer  would  be  too  frequently  stopped  by  pieces  of  paper, 
or  by  other  legitimate  sewage  matter;  and  because  it  would 
be  too  difficult  of  access  for  inspection  and  cleaning.  The 
last  two  objections  could,  it  is  true,  be  met  theoretically  by 
making  the  house-connection  of  a  size  so  much  smaller  that 
nothing  could  pass  it  which  would  obstruct  the  sewer.  But 
such  construction  would  be  utterly  impracticable. 

There  is  no  particularly  good  reason,  however,  why  a 
house-connection  might  not  be  made  of  2-inch  pipe  and  the 
sewer  of  3-inch  or  4-inch;  and  systems  are  in  existence  and 
reported  working  satisfactorily  where  such  sizes  are  in  use. 
But  such  construction  would  generally  compel  a  change  in  the 
stock  dimensions  of  all  house- plumbing  and  connected  appli- 


64  SEWERAGE. 

ances,  and  give  rise  to  inconveniences  more  than  balancing 
the  saving  in  cost.  A  4-inch  house-connection  is,  however, 
ample  for  any  building  containing  less  than  50  persons  and 
which  contributes  only  ordinary  house-sewage  (see  Art.  82). 

The  sewer  might,  then,  where  the  grade  is  quite  steep,  be 
constructed  as  a  4-inch  pipe  from  the  head  to  such  point  as 
the  calculations  fix  for  an  increase  in  size;  but  it  is  better  to 
make  the  minimum  diameter  6  or  8  inches,  for  then  there 
would  be  less  probability  that  anything  passing  the  house-con- 
nection, in  which  the  velocity  may  be  considerable,  would 
obstruct  the  sewer.  It  is  thought  that  the  weight  of  evidence 
tends  to  show  that  with  4-inch  house-connections  8-inch 
sewers  are  obstructed  much  less  frequently  than  are  6-inch. 
Among  other  reasons  for  this  is  the  fact  that  a  6-inch  stick, 
chicken-bone,  etc.,  will  pass  a  4-inch  trap,  but  an  8-inch  one 
will  not;  and  that  a  6-inch  stick  is  more  apt  to  become 
wedged  across  a  6-inch  pipe  than  across  an  8-inch  one.  Some 
engineers  set  the  6-inch,  more,  probably,  the  8-inch  pipe, 
as  the  minimum  to  be  employed  for  sewers.  In  England 
9  inches  is  generally  the  minimum  size. 

In  the  case  of  storm-sewers  the  only  change  of  conditions 
affecting  the  volume  of  sewage  which  is  likely  to  occur  is  in 
the  imperviousness  of  the  contributing  area.  If  this  is  taken 
at  the  maximum,  as  for  a  business  district,  no  allowance  need 
be  made.  In  any  case  the  allowance  for  change  can  best  be 
made  in  the  selection  of  the  factor  of  imperviousness  and  the 
sewer  built  of  corresponding  capacity.  It  is  probable  that  no 
condition  of  size  or  character  of  tributary  area  will  in  actual 
practice  call  for  a  storm-sewer  of  a  diameter  less  than  10  or 
12  inches.  It  should,  if  possible,  be  of  a  diameter  at  least  as 
great  as  that  of  the  largest  opening  in  the  storm-water  inlets, 
to  prevent  sticks  lodging  across  it. 

A  circular  or  egg-shaped  sewer  is  sometimes  limited  in  size 
by  the  amount  of  covering  necessary  and  the  distance  below 


FLO  W  IN   SEWERS.  65 

the  street-surface  of  its  invert,  where  this  is  fixed  by  the  eleva- 
tion of  the  outlet  and  the  necessary  grade  from  that  to  the 
point  in  question.  If  the  whole  sewer  at  this  point  be  lowered, 
the  grade  and  velocity  become  less  and  the  size  of  the  sewer 
must  be  increased,  thus  raising  the  crown.  The  size  can  be 
reduced  only  by  increasing  the  grade,  which  means  raising 
the  sewer.  Under  these  conditions  the  sewer  can  be  built  as 
an  "  inverted  siphon  "  to  flow  under  a  head  (Art.  38),  two  or 
more  parallel  sewers  can  be  substituted  for  the  one,  or  the 
shape  can  be  modified.  In  adopting  the  last  alternative 
engineers  have  devised  many  forms  which  can  be  generally 
classified  as  those  flattened  on  the  bottom  and  those  flattened 
at  the  top. 

ART.  19.     SHAPE  OF  SEWERS. 

Of  all  possible  shapes  of  sewers  of  equal  area  of  cross-sec- 
tion the  circular  gives  the  greatest  velocity  when  flowing  full 
or  half  full  and,  having  the  shortest  perimeter,  contains  the 
least  material.  Also,  being  devoid  of  angles,  it  offers  little 
opportunity  for  deposits.  For  sewers  intended  to  always  flow 
at  least  half  full  it  is  therefore  the  most  desirable  shape. 
This  is  not  true,  however,  of  a  combined  sewer — that  is, 
one  which  carries  both  house-sewage  and  storm-water — 
for,  as  we  have  seen  (Art.  22),  the  house-sewage  may  occupy 
only  -3-^  of  the  capacity  of  the  sewer  and  have  a  velocity  only 
about  ^  as  great  if  a  circular  sewer  be  used.  If  the  sewer, 
considered  as  a  storm-sewer,  be  given  a  grade  adapted  to  a 
velocity  of  4  feet  per  second  when  flowing  full  or  half  full  the 
velocity  of  the  house-sewage  would  be  about  |  of  a  foot  per 
second.  If  on  the  other  hand  the  grade  be  so  increased 
(which  is  seldom  possible)  as  to  give  the  minimum  house- 
sewage  flow  a  velocity  of  i£  feet  per  second  the  depth  of  this 
flow  would  be  only  about  .02  of  the  sewer  diameter.  Neither 
of  these  conditions  is  permissible  in  a  good  sewerage  system. 


66 


SE  WERA  GE. 


The  result  of  adopting  too  flat  a  grade  is  shown  by  the 
illustration  (Plate  VII,  Fig.  8)  of  obstructions  in  the  old 
London  sewers,  which  came  to  be  known  as  "  sewers  of 
deposit."  These  required  frequent  cleaning,  since  almost 
the  entire  sewage  matter  was  deposited  in  them,  and  became 
very  dangerous  to  the  health  of  the  city.  The  question  thus 
forced  upon  the  attention  of  engineers  was  first  solved  by 
building  in  the  bottoms  of  the  old  sewers  channels  of  much 
shorter  radius  of  curvature  (Plate  VII,  Fig.  7).  These,  by 
increasing  R  and  consequently  V,  as  well  as  the  depth  of  flow 
relative  to  the  invert  radius,  had  the  same  effect  upon  the  flow 


e 


FIG.  2. — EGG-SHAPED  SEWER. 

as  the  use  of  smaller  sewers,  which  they  in  fact  were,  and 
answered  the  purpose,  practically  the  same  design  being  still 
employed  in  Washington,  D.  C.,  and  other  American  cities. 
It  will  be  noticed,  however,  that  there  is  considerable  useless 
material  in  this  design;  also  that  the  bench  on  either  side  of 
the  small  channel  offers  opportunity  for  the  deposit  of 
material,  which  may  there  putrefy.  To  meet  these  objections 
the  egg-shaped  sewer  was  designed  and  is  used  extensively 
for  combined,  and  sometimes  for  storm-water,  sewers.  Several 


FLOW  IN   SEWERS.  67 

proportions  have  been  suggested  and  used,  but  that  most 
frequently  found  in  modern  American  practice  is  represented 
here.  The  diameter  of  a  circular  sewer  having  an  equal  area 
is  1.  209/2.  In  this  sewer 

//=  i.  5  A  dcorr'    =  0.5  D, 

eforr  =  i.$D,  gh  or  r"  — 


Reference  to  Table  No.  14  shows  that  a  flow  of  yj-g  of  the 
full  capacity  of  this  sewer  would  have  a  velocity  about  0.3  as 
great  as  if  the  sewer  flowed  full,  or  85$  greater  than  the  same 
amount  in  a  circular  sewer  of  equal  total  capacity;  also  the 
depth  would  be  about  o.  iZ>,  or  0.4?"".  If  the  velocity  of  the 
house-sewage  in  the  above  be  2  £  feet  per  second  (as  it  should 
be)  that  when  the  sewer  were  full  would  be  8  feet  or  more 
per  second.  This  form  does  not,  therefore,  quite  meet  the 
requirements  of  a  combined  sewer,  intended  to  carry  a  run-off 
of  3  inches  from  the  area  drained,  as  to  either  depth  or 
velocity  of  house-sewage.  As  we  shall  see  later,  this  require- 
ment applies  to  lateral  combined  sewers  only,  and  this  design 
is  suitable  for  most  combined-sewer  mains,  whose  maximum 
flow  is  only  ij  or  2  inches  run-off  from  the  drainage-area. 
In  laterals  or  other  sewers,  however,  where  the  proportion  oi 
house-  to  storm-sewage  will  be  too  small,  or  for  some  othei 
reason  sufficient  velocity  and  depth  for  the  house-sewage 
cannot  be  thus  obtained,  the  adoption  of  an  egg-shaped  sewei 
with  r"  =  \D  or  \D,  or  a  form  similar  to  that  shown  in  Plate 
VII,  Fig.  2,  is  recommended,  the  purpose  being,  whatever 
the  form  adopted,  to  get  a  satisfactorily  high  value  for  R  for 
the  house-sewage  flow.  Whatever  the  radius  of  invert  the 
grade  must  not  be  less  than  that  which  would  be  required 
by  a  circular  house-sewer  having  a  radius  =  r"  .  The 
radius  r"  should  be  so  chosen,  also,  that  the  depth  of  house- 

r" 
sewage  will  never  be  less  than    —  .     A  flat   bottom   should 


68  SEWjERAGE. 

never  be  used  for  house  or  combined  sewers  unless  the 
sewage  will  always  be  sufficient  to  cover  it  at  least  6  inches 
deep.  Angles  in  the  section  are  to  be  avoided  as  favoring 
deposits.  In  storm-sewers  it  is  advisable  that  the  shape  be 
such  as  to  give  good  velocity  to  small  amounts  of  storm- 
water,  but  the  penalty  of  not  following  this  rule  is  not  so 
serious  as  in  the  case  of  house-sewers. 


CHAPTER  IV. 
FLUSHING   AND   VENTILATION.          ^ 

ART.   20.      NECESSITY  FOR  FLUSHING. 

IT  is  seen  from  Table  No.  13  that  if  at  any  time  the  flow 
in  a  circular  sewer  becomes  less  in  volume  than  -^fo  of  the  full 
capacity  of  the  sewer  the  depth  becomes  less  than  J  the 
diameter  and  the  velocity  less  than  •£  that  for  a  full  sewer. 
If  the  sewer  is  small  the  first  condition  is  apt  to  cause 
deposits  by  the  stranding  of  floating  matter  on  the  edges  or 
even  in  the  centre  of  the  stream;  if  the  grade  is  near  the 
minimum  the  velocity  becomes  less  than  is  desirable  and 
deposits  result  from  this  cause.  But  a  6-inch  or  8-inch  pipe 
is  usually  the  minimum  size  employed  and  is  carried  up  to  the 
last  house-connection,  from  which  a  quantity  of  sewage  very 
much  less  than  -££$  of  the  full  sewer  capacity  is  received.  In 
fact  there  will  be  in  a  residence  district  a  stretch  of  at  least 
400  feet  of  6-inch  or  700  feet  of  8-inch  sewer,  even  at  the 
flattest  allowable  gfrade,  which  would  be  filled  less  than  y1^  of 
its  capacity  by  a  rate  of  175  gallons  per  capita,  and  conse- 
quently where  deposits  are  probable.  The  discharge  from  any 
individual  house  comes  usually  not  in  a  continuous  flow,  how- 
ever, but  in  spurts  of  relatively  large  quantities  separated  by 
considerable  intervals  of  time.  If  we  watch  such  intermittent 
discharge  we  will  find  that  when  the  sewage  enters  an  empty 
sewer  from  the  house-connection  it  flows  both  down  the 
grade  and  also  up  it  for  a  short  distance.  The  latter  portion 

69 


70  SEWERAGE, 

at  the  end  of  the  discharge  also  flows  down  grade,  but  it  has 
probably  carried  with  it  and  left  at  the  upper  limit  of  its  flow 
matter  which  remains  there  to  putresce  and  perhaps  form  the 
beginning  of  an  obstruction.  Beginning  in  the  sewer  at 
practically  nothing  (since  most  of  the  initial  velocity  is 
destroyed  by  foaming),  the  velocity  of  such  discharge  contin- 
ually increases,  and  the  depth  decreases,  with  the  distance 
from  the  point  of  entry.  This  frequently  causes  the  strand- 
ing below  the  house-connection  of  large  floating  matter  which 
is  introduced  from  such  connection,  and  although  successive 
discharges  may  move  this  matter,  each  one  a  little  further 
down  the  sewer,  a  long  cessation  of  them  may  give  it  an 
opportunity  to  become  fixed  in  its  position.  Discharges  from 
connections  higher  up  the  grade  will  tend  to  prevent  these 
deposits,  two  or  more  discharges  occasionally  coming  simul- 
taneously and  uniting  their  volume;  and  generally  the  further 
any  connection  is  from  the  upper  or  dead  end  of  a  branch  the 
less  the  danger  of  its  causing  such  deposits.  In  a  thickly 
settled  district  this  danger  in  the  case  of  6-  or  8-inch  pipe 
becomes  very  small  at  a  point  to  which  there  is  tributary 
IOOO  to  1500  feet  of  sewer.  If  the  district  is  sparsely  settled, 
however,  the  danger  may  exist  for  many  times  this  length. 

Any  house-sewer,  but  particularly  a  lateral,  is  liable  to 
partial  stoppage  at  times,  due  to  ashes,  sand,  or  other 
material  introduced  through  house-connections,  manholes,  or 
infiltering  through  the  joints  or  other  defective  places. 
Unless  the  velocity  of  flow  is  sufficient  to  carry  this  matter 
along  it  will  form  deposits  in  the  sewer-invert  which  must  be 
in  some  way  removed. 

There  is  another  class  of  deposits,  composed  of  mycelial 
matter,  which  forms  in  most  house-sewers.  This  contracts 
the  area  of  cross-section  and  may  become  the  breeding-place 
of  micro-organisms;  but  emits  little  odor  and  is  readily  de- 
tached and  carried  away  by  a  strong  flush  of  water. 


FLUSHING   AND    VENTILATION.  71 

To  prevent  these  deposits  the  only  practicable  way  known 
is  to  keep  all  sewers  constantly  flowing  with  a  depth  at  least 
£  the  radius  of  the  invert,  water  being  introduced  for  this 
purpose  if  necessary,  and  also  to  maintain  a  velocity  of  at 
least  ij  feet  per  second.  To  remove  them  the  methods 
employed  are  either  to  occasionally  turn  through  the  sewer 
streams  of  water  of  sufficient  quantity  and  velocity  to  dislodge 
and  remove  the  deposits,  or  to  employ  shovels,  hoes, 
"  pills,"  scrapers,  or  similar  appliances  to  be  described  in.- 
Chapter  XV. 

The  method  of  prevention,  if  applied  near  a  dead  end, 
where  the  sewage  flow  is  minimum  in  quantity,  even  in  the 
case  of  a  sewer  laid  at  minimum  grade,  would  require  about 
47,000  gallons  per  day  for  each  line  of  6-inch  pipe  and  83,000 
gallons  for  each  8-inch  line.  These  quantities  it  will  usually 
be  impracticable  to  supply;  and  were  it  practicable  the  addi- 
tion to  the  sewage  of  this  amount  in  each  of  several  branches 
would  compel  a  large  increase  in  the  size  of  the  sewer-mains, 
and  greatly  increase  the  cost  of  treatment  in  case  this  method 
of  disposal  was  employed.  There  will  occasionally  be  in- 
stances, however,  where  a  convenient  stream  of  water  can 
be  utilized  to  advantage  in  this  way. 

It  sometimes  happens  that  an  old  sewer-main  or  other 
large  drainage-channel  is  at  so  flat  a  grade  as  to  be,  in  part  at 
least,  a  sewer  of  deposit.  Flushing  can  be  used  to  advantage 
in  such  a  case  to  stir  up  and  remove  the  matter  deposited. 
A  notable  instance  of  this  may  be  found  at  Milwaukee,  Wis., 
where  40,000  gallons  of  lake-water  per  minute  are  pumped 
into  the.  Milwaukee  River  (the  flow  of  which  is  largely  sewage) 
for  flushing  it. 

In  general  a  sewer  in  which  there  is  a  continuous  flow 
with  a  depth  of  at  least  £  the  radius  of  the  invert  and  a 
velocity  exceeding  2  feet  will  need  but  infrequent  cleaning  if 
legitimate  sewage  only  be  admitted.  If  for  any  reason  or  at 


72  SEWERAGE. 

any  time  these  conditions  be  not  fulfilled  artificial  cleaning 
will  probably  need  to  be  resorted  to. 


ART.  21.     METHODS  OF  FLUSHING. 

As  stated,  there  are  two  general  methods  of  cleaning 
sewers:  flushing,  and  by  the  use  of  some  kind  of  scraper  or 
similar  tool.  The  latter  usually  calls  for  no  special  provisions 
in  the  construction  and  will  be  treated  of  in  Part  III. 
Flushing,  however,  is  frequently  accomplished  by  appliances 
built  into  the  system,  and  the  principles  involved  are  other 
than  those  controlling  hand  labor;  it  is  therefore  necessary  to 
consider  it  in  designing.  Flushing  may  be  done  by  hand,  by 
automatic  appliances,  or  by  use  of  rain-water. 

By  the  first  the  sewer  can  be  flushed  from  any  manhole, 
as  well  as  from  flush-tanks;  by  the  second  from  fixed  points 
only,  usually  the  heads  of  laterals;  by  the  third  the  flushing- 
water  enters  from  roofs  through  all  or  many  house-connec- 
tions, *r  in  some  instances  the  inlets  are  so  constructed  as  to 
st^re  the  rain-water  from  the  street-surfaces  or  from  water- 
courses and  flush  with  periodic  discharges  of  the  same. 

The  secret  of  successful  flushing  lies  in  compelling  a  large 
mass  of  water  to  move  at  considerable  speed  down  the  sewer. 
If  the  sewer  be  less  than  24  inches  or  30  inches  in  diameter 
water  should  as  far  as  possible  completely  fill  it,  that  deposits 
may  be  removed  from  its  entire  circumference  and  also  that 
the  effect  of  the  flush  may  be  felt  far  down  the  sewer.  With 
the  sewer  flowing  full  bore  at  the  upper  end  the  depth  of  the 
water  will  decrease  as  the  flushing-wave  progresses  down  the 
sewer,  until  at  some  point  below,  at  a  distance  varying  with 
the  size  and  grade  of  the  sewer,  with  the  head  of  water  at  the 
upper  end  and  the  volume  of  sewage  flowing,  the  depth  and 
velocity  of  the  sewage  will  be  but  little  affected  by  the  flush. 

The  initial  velocity  will  depend  upon  the  head  and  upon 


FLUSHING  AND    VENTILATION.  73 

the  facility  offered  the  water  for  entering  the  sewer.  There 
should  be  a  free  and  open  orifice  at  the  entrance  end,  and  if 
possible  the  angle  between  the  inside  of  the  sewer  and  that 
of  the  manhole  or  flush-tank  should  be  rounded.  Speed  is  of 
as  much  value  in  flushing  as  quantity,  and  with  a  given 
amount  of  flushing-water  the  more  quickly  it  can  be  made  to 
pass  through  the  sewer  the  better.  In  most  cases  little 
if  any  benefit  would  result  should  a  faucet  be  left  con- 
tinuously running  in  each  house  in  a  city,  but  y^Vir  °f  tne 
same  amount  of  water  used  in  a  proper  way  would  be  of  great 
benefit  to  the  system. 

Although  for  creating  velocity  the  head  in  the  flush-tank 
should  generally  be  as  great  as  possible,  it  must  be  limited  by 
the  amount  of  internal  pressure  which  the  sewer  can  stand 
without  rupture.  A  few  years  ago  a  brick  sewer  in  Washing- 
ton, D.  C.,  was,  on  account  of  insufficient  size,  put  under 
.such  a  head  of  water  by  the  run-off  from  a  cloudburst  that 
its  upper  half  was  completely  severed  from  the  lower  and  the 
sewer  destroyed,  and  a  similar  result  might  follow  from  too 
great  pressure  of  flushing-water.  With  a  pipe  sewer  this 
danger  is  not  so  great.  A  head  of  6  or  8  feet  at  the  manhole 
or  flush-tank — which  is  more  than  can  usually  be  obtained — 
should  not  endanger  a  pipe  sewer.  Brick  sewers  as  ordinarily 
constructed  should  not  be  filled  to  a  point  more  than  5  feet 
above  the  invert  or,  for  those  more  than  5  feet  in  diameter, 
higher  than  the  crown.  In  no  case  should  the  water  be 
backed  up  a  sewer-line  to  such  a  height  as  would  flood  any 
connected  cellars. 

The  flushing-water  should  move  down  and  not  up  the 
sewer,  since  the  effect  of  the  latter  would  probably  be  to 
sweep  the  intermediate  deposits  nearly  to  the  upper  limit  of 
the  wave  and  leave  them  there  to  dam  the  flow.  The  inter- 
val which  should  elapse  between  flushings  will  vary  under 
different  conditions.  In  sewers  where  there  is  a  constant 


74  SEWERAGE. 

ample  flow  of  water,  where  stoppages  are  few  and  due  solely 
to  accident  or  design  of  ignorant  or  malicious  persons,  flushing 
need  be  resorted  to  only  when  such  stoppages  occur.  If  it  is 
found  from  experience  that  stoppages  are  frequent  or  that 
there  is  a  constant  depositing  of  material  in  the  sewers,  or  if 
it  is  foreseen  that  this  will  occur  from  causes  mentioned  in 
the  previous  article,  frequent  flushings  should  be  provided  for. 

In  the  case  of  a  dead  end  of  a  house  or  combined  sewer, 
or  one  which  has  but  few  house-connections  made  with  it,  the 
flushing  should  be  done  once  in  each  24  or  at  least  48  hours. 

Both  separate  and  combined  systems  have  been  built  and 
satisfactorily  maintained  without  flushing  at  any  point  oftener 
than  two  or  three  times  a  year.  It  is  probable  that  this  is 
possible  only  where  there  is  considerable  ground-water  enter- 
ing the  sewers  at  their  upper  ends,  or  where  the  dead  ends 
occur  only  in  thickly  populated  districts  and  on  grades  a 
little  greater  than  the  minimum  herein  advocated.  There  is 
too  little  definite  information  on  this  subject  to  justify  a  posi- 
tive statement  as  to  when,  if  ever,  flushing  at  dead  ends  may 
be  profitably  omitted.  It  is  advisable  so  to  arrange  every 
house  or  combined  sewer,  where  the  conditions  will  be  those 
given  as  favoring  deposits,  that  it  can  be  satisfactorily  flushed. 

A  few  experiments  have  been  made  on  the  actual  effect 
of  flushing-water  in  a  sewer,  chiefly  with  reference  to  the 
velocity  and  depth  of  the  flushing-water  at  different  distances 
from  the  point  of  entering.  Andrew  Rosewater  found  by 
experiment  with  a  4OO-gallon  tank  at  the  head  of  an  8-inch 
line  of  sewer  discharging  1 1  gallons  per  second  that  at  the 
first  manhole,  200  feet  below  the  flush-tank,  the  water  was 
6  inches  deep  and  had  a  velocity  of  5.6  feet  per  second;  200 
feet  further  the  depth  was  5  inches,  velocity  2.8  feet;  and 
400  feet  further  the  depth  was  4  inches,  velocity  2  feet — 
showing  the  flushing  effect  to  be  practically  exhausted  in  800 
feet.  Mr.  Ogden,  in  experiments  made  in  Ithaca,  N.  Y., 


FLUSHING   AND     VENTILATION.  75 

in  1897,  found  that  with  discharges  from  flush-tanks  through 
8-inch  pipes  of  from  .89  to  i.i  cubic  feet  per  second  the  flow 
was  reduced  to  2  inches  at  1123  feet  from  the  flush-tank  in 
two  cases  where  the  grades  varied  from  .52$  to  1.31$,  at 
about  1000  feet  in  another  where  the  grades  varied  from 
i. 02$  to  3.14^,  and  in  another  where  the  grades  varied  from 
.80$  to  .89$  the  depth  was  4  inches  at  895  feet  from  the 
flush-tank.  In  the  first  two  the  sewer  was  scoured  clean  for 
529  feet  and  some  effect  felt  at  819  feet;  in  the  third  the 
sewer  was  cleaned  for  556  feet  and  the  effect  slight  at  970 
feet;  in  the  last  the  pipe  was  "  disturbed,  but  not  cleaned," 
at  636  feet,  until  600  gallons  were  discharged,  when  it  was 
cleaned  for  more  than  636  feet,  but  less  than  900  feet.  The 
other  discharges  referred  to  were  of  300  gallons  each.  An 
interesting  series  of  experiments  were  conducted  and  their 
results  plotted  by  S.  H.  Adams  in  England.  These  appeared 
to  show,  as  do  the  above,  that  300  gallons  is  in  some  cases 
insufficient  to  properly  flush  an  8-inch  pipe;  also  that  the 
effect  of  such  a  quantity  is  felt  for  about  800  to  1000  feet.* 

In  flushing  by  hand  the  sewer  is  usually  stopped  at  the 
down-grade  side  of  a  manhole  or  flush-tank,  this  is  filled  to  a 
desired  height  with  water  or  by  allowing  the  sewage  to 
accumulate  in  and  above  it,  the  gate,  plug,  or  other  stopper 
is  removed  and  the  water  allowed  to  enter  the  sewer  under 
the  head  due  to  its  height.  Where  outside  water  is  used  for 
flushing  and  is  limited  in  quantity  another  stopper  should  be 
placed  at  the  upper  orifice  in  manholes,  to  prevent  a  flow  up 
the  sewer,  and  left  in  until  the  flushing  is  over.  The  stoppers 
are  made  of  various  forms  and  to  act  in  various  ways,  and  to 
close  the  whole  or  only  the  lower  half  or  two  thirds  of  the 
sewer.  The  water  is  obtained  from  different  sources  and 
introduced  by  different  methods,  a  further  discussion  of  which 
will  be  given  in  Part  III. 

In  England  the  separate  system,  when  first  constructed, 

*  See  also  Transactions  Am.  Soc.  C.  E.,  vol.  XL,  pp.  1-30. 


76  SEWERAGE. 

was  designed  to  admit  to  the  house-sewers  roof-water  and 
drainage  from  yards,  and  this  method  is  still  followed  there 
to  a  considerable  extent.  In  the  United  States  the  majority 
of  separate  systems  are  not  supposed  to  receive  this  water. 
It  is  argued  by  advocates  of  the  former  practice  that  the 
householder  should  not  be  required  to  construct  two  connec- 
tions, one  for  house-sewage  and  one  for  rain-water.  But  the 
last  can  be  conveniently  discharged  into  the  gutter,  except 
in  the  case  of  buildings  covering  a  large  area,  when  the  cost 
of  the  extra  drain  would  be  relatively  inappreciable. 

Another  argument  for  the  admission  of  roof-water  is  that 
it  is  beneficial  in  flushing  the  sewer.  If  it  is  admitted  only 
at  and  near  the  dead  ends  it  will  usually  be  advantageous,  but 
it  should  not  be  thought  to  take  the  place  of  all  other  flush- 
ing. The  sewers  are  most  likely  to  need  flushing  at  dry 
seasons,  and  this  must  then  be  done  by  hand  or  otherwise. 
There  is  a  danger  that  the  presence  of  these  roof-connections 
will  give  a  false  idea  that  the  flushing  requirements  have  been 
entirely  met. 

If  roof-water  is  admitted  to  small  sewers  throughout  their 
length  there  is  great  probability  of  its  gorging  the  pipes  and 
backing  up  into  connected  basements  and  cellars.  In  Mount 
Vernon,  N.  Y.,  in  1892  great  damage  was  caused  in  this  way 
and  all  roof-drains  were  at  once  disconnected ;  and  many 
similar  instances  might  be  cited. 

Since  the  danger  is  so  imminent  and  the  benefits  con- 
tributed at  such  uncertain  intervals,  most  American  engineers 
do  not  advise  the  admission  of  roof-water  to  small  sewers. 

Sewers  are  sometimes  flushed  by  connecting  their  upper 
ends  with  convenient  streams,  or  artificial  channels  filled  from 
such  streams,  the  water  being  admitted  periodically  by  gates: 
as  at  Bern,  Wurzburg,  Innsbruck,  Freiburg,  Breslau,  Munich, 
and  other  cities  of  Europe;  also  at  Newton,  Mass. 

Reservoirs  fed  by  streams  or  springs  are  used  in  Munich, 


FLUSHING   AND    VENTILATION.  77 

Cologne,  Wiesbaden,  Frankfurt,  Stuttgart,  and  other  cities. 
At  the  first-mentioned  place  large  underground  reservoirs, .one 
of  which  is  6  feet  6  inches  by  4  feet  7  inches  and  extends  along 
two  blocks,  are  filled  from  the  Isar  River. 

Tides  are  sometimes  made  use  of  for  this  purpose,  the 
water  being  allowed  to  rise  in  the  sewer  at  high  tide  and 
being  held  there  by  gates  until  the  low  tide,  when  it  is 
released.  Ordinarily  only  the  lower  reach  of  the  outlet  sewer 
can  be  thus  flushed.  A  better  method  in  some  cases  is  to 
hold  the  water  after  high  tide  in  a  basin  from  which  it  is 
rapidly  discharged  at  low  tide  into  the  sewers  to  be  flushed. 

As  in  the  case  of  Milwaukee,  already  cited,  and  of  Bre- 
men, the  flushing-water  may  be  pumped  from  a  lake  or  river 
directly  to  the  sewer.  This  is  of  course  applicable  within  the 
limits  of  economy  to  very  large  sewers  only,  or  to  a  system 
where  a  number  of  dead  ends  can  be  reached  by  a  compara- 
tively short  line  of  water  pipe. 

The  water  for  flushing  is  sometimes  taken  from  the  ocean 
or  other  body  of  salt  water;  but  the  salts  are  thought  to 
decompose  the  sewage,  giving  rise  to  gases  and  deposits  of 
matter  rendered  insoluble,  and  are  corroding  to  any  metal- 
work  in  the  sewers.  Hence  its  use  is  not  advised  by  most 
authorities. 


ART.  22.     APPLIANCES  FOR  FLUSHING. 

Automatic  flush-tanks  are  in  use  in  a  large  number  of  sep- 
arate systems,  but  are  seldom  used  for  flushing  combined  or 
storm-wattr  sewers,  owing  to  the  enormous  quantities  of 
water  needed  for  that  purpose.  There  have  been  a  great 
number  of  devices  invented  for  flushing.  Most  of  those  at 
present  used  in  any  considerable  numbers  are  siphons  in  prin- 
ciple, so  arranged  that  a  tank  in  which  they  are  set  may  fill 
gradually  up  to  a  certain  point,  when  its  contents  are  dis- 


78  SEWERAGE. 

charged  rapidly  into  the  sewer.  The  tanks  are  made  to  con- 
tain at  the  time  of  discharge  from  150  to  600  or  even  1200 
gallons  for  6- to  lo-inch  pipe  sewers.  For  larger  sewers  larger 
quantities  are  provided.  The  smaller  quantities  are  of  little 
use.  No  tank  should  discharge  less  than  250  gallons  at  a  time 
into  a  6-inch  pipe,  and  correspondingly  larger  amounts  into 
larger  sewers.  500  to  800  gallons  discharged  into  an  8-inch 
pipe  once  in  24  hours  would  be  more  beneficial  than  half  of 
that  amount  at  each  of  three  or  four  discharges  during  the 
same  time.  The  tanks  should,  of  course,  be  water-tight. 
They  are  usually  built  of  brick  plastered  on  both  the  inside 
and  the  out,  or  of  concrete  with  steel  rods.  Wood  or  iron  could 
be  used,  but  would  not  be  so  durable.  They  should  be  so 
built  and  arranged  that  the  water  may  have  the  greatest  per- 
missible head  above  the  sewer  when  discharging.  (For  details 
see  Art.  42.) 

The  water  may  be  conveniently  admitted  to  the  tank 
through  a  half-inch  or  smaller  stop-cock  connected  with  the 
street-main  by  a  supply-pipe  passing  through  the  tank-wall. 
This  cock  is  continually  left  sufficiently  open  to  cause  the 
tank  to  fill  and  discharge  at  desired  intervals.  If  the  water  is 
inclined  to  be  muddy  at  times  the  use  of  too  large  a  supply- 
pipe  will  result  in  the  choking  of  it  by  sedimentation.  It 
should  be  of  such  a  size  that  the  quantity  to  be  used  in  the 
tank  will  pass  through  it  with  a  velocity  of  2  feet  per  second 
or  more.  Instead  of  a  cock,  a  small  orifice  plate  is  sometimes 
placed  at  the  end  of  the  pipe,  the  size  of  orifice  determining 
the  flow. 

The  discharge-pipe  of  the  tank  should  be  at  least  as  large 
as  the  sewer.  It  would  be  better  to  have  it  a  size  or  two 
larger  and  bell-mouthed  at  the  end. 

The  automatic  flushing  appliances  most  in  use  in  the 
United  States  are  further  referred  to  in  Chapter  VIII.  They 


FLUSHING   AND    VENTILATION.  79 

are,  most  of  them,  covered  by  patent,  and  the  prices  range 
upward  from  about  $12  fora  tank  to  discharge  150  gallons 
through  a  5-inch  pipe. 

Where  automatic  flush-tanks  are  not  used  some  engineers 
have  built  into  manholes  at  dead  ends  2-inch  to  4-inch  pipes 
connected  with  adjacent  water-mains  and  provided  with  gate- 
valves,  as  at  Mount  Vernon,  N.  Y,,  and  Newton,  Mass. 
This. is  probably  the  most  convenient  method  of  hand-flushing 
and  the  cheapest  to  operate.  The  cost  at  Mount  Vernon  was 
about  $40  for  each  4-inch  branch  and  connection. 

There  are  numerous  methods  of  flushing  by  hose,  by 
water-tanks,  etc.,  many  of  which  are  described  in  Part  III. 

In  flushing  by  rain-water  no  special  appliances  are  ordi- 
narily used,  the  roofs  and  sometimes  the  yards  being  con- 
nected in  the  ordinary  way  with  the  sewer. 

Special  methods  involving  pumping,  some  instances  of 
which  have  been  referred  to,  need  no  description,  since  the 
details  will  vary  with  each  case. 


ART.  23.      NECESSITY  FOR  VENTILATION. 

In  every  sewer  there  is  a  space  above  the  sewage  filled 
with  air,  and  this  air,  it  is  evident,  will  generally  be  far  from 
pure  unless  kept  in  motion  and  frequently  renewed.  The 
odor  accompanying  all  sewage,  even  when  there  is  no  decom- 
position proceeding  in  the  sewer,  is  communicated  to  this  air, 
and  there  will  frequently  be  given  off  some  gases  due  to 
putrefaction.  This  air  probably  is  seldom  motionless.  It  is 
influenced  by  the  sewage  to  move  down  the  sewer;  it  is  warmer 
in  winter  and  sometimes  in  summer  than  the  outside  air, 
which  condition  occasions  motion  when  there  is  communica- 
tion between  the  two;  it  is  driven  out  of  or  along  the  sewer 
by  sudden  inflows  of  sewage  from  house-connections  or  branches 


8o  SEWERAGE. 

and  sucked  in  by  decrease  in  the  volume  of  flow;  near  the 
outlet  the  direction  and  force  of  the  wind  affect  it,  driving 
it  up  the  sewer  or  sucking  it  out;  last,  and  most  im- 
portant, it  passes  into  empty  or  partly  empty  house-connec- 
tions and  into  proximity  to,  if  not  into  the  air  of,  connected 
residences.  Herein  lies  the  danger.  There  is  no  "  sewer- 
gas  "  which  is  deadly  to  human  life,  but  it  is  known  that  air 
which  has  been  confined  in  contact  with  decomposing  sewage 
is  charged  with  "  an  ever- varying  mixture  of  gases;  and  of 
those  that  are  deleterious  the  more  prominent  are  sulphuretted 
hydrogen,  sulphide  of  ammonium,  and  caburetted  hydrogen; 
while  ammonia,  carbonic  acid,  and  occasionally  carbonic  oxide 
derived  from  leakage  of  illuminating-gas  into  sewers  are 
present  in  more  or  less  large  proportions."  (W.  P.  Gerhard, 
"  Sanitary  House  Inspection.") 

The  least  that  can  be  said  of  these  is  that  they  lessen  the 
vitality  and  prepare  the  way  for  easy  conquest  by  diseases 
that  might  otherwise  obtain  no  hold  upon  the  system;  they 
should  therefore  be  excluded  from  all  occupied  buildings. 
The  danger  due  to  impure  air  in  dwellings  has  led  the  New 
York  Board  of  Health  to  conclude  that  "  40%  of  all  deaths  are 
caused  by  breathing  impure  air."  Playfair  asserts  that  in 
modern  hygiene  "  nothing  is  more  conclusively  shown  than 
the  fact  that  vitiated  atmospheres  are  the  most  fruitful  sources 
of  disease."  Death  rates  have  been  "  reduced  in  children's 
hospitals  from  50$  to  5$  by  improved  ventilation." 

While  the  vitiation  referred  to  in  these  quotations  is  not 
that  of  sewer-air  exclusively,  this  is  included  among  the 
causes  of  it  and  produces  the  same  effect.  Unfortunately  the 
most  numerous  and  fruitful  sources  of  the  gases  are  found, 
not  in  the  sewer,  but  in  the  house-connections  or  soil-pipes, 
and  consequently  not  directly  under  the  control  of  the 
authorities.  The  methods  necessary  to  prevent  danger  from 


FLUSHING   AND    VENTILATION.  £i 

these  sources  will  be  considered  under  the  head  of  House- 
connections  (Art.  82). 

ART.  24.     METHODS  OF  VENTILATION. 

It  is  evident  that  the  danger  from  sewer-air  may  be 
avoided,  or  at  least  lessened,  in  two  ways:  by  preventing  the 
ci cation  of  gases,  and  by  preventing  the  sewer-air  from  reach- 
ing human  beings  in  dangerous  quantities  or  under  dangerous 
conditions.  No  method  has  yet  been  found  for  perfectly 
accomplishing  either  of  these  aims  in  practice,  but  both  may 
be  partially  attained. 

Aside  from  illuminating-gas  most  of  the  objectionable 
gases  are  given  off  by  putrefaction,  and  the  prevention  of  this 
in  the  sewers  is  therefore  most  necessary.  This  is  best 
accomplished  by  the  removal  of  all  sewage  to  the  outlet  before 
putrefaction  can  begin;  and  here  is  seen  the  advantage  of 
daily  flushing,  cleaning  the  upper  laterals  of  deposits  before 
they  reach  this  dangerous  stage.  The  use  of  disinfectants  in 
sewage  for  this  purpose  is  seldom  advisable,  both  on  account 
of  the  enormous  cost  and  practical  difficulties  of  applying 
them  and  because  the  various  and  changing  characters  of 
sewage  in  different  cities  and  from  hour  to  hour  may  intro- 
duce such  matter  as  will  combine  with  any  given  disinfectant 
to  produce  deposits  and  gases  fully  as  injurious  as  those  due 
to  sewage  alone.  The  presence  of  objectionable  germs  in 
sewer-air  is  probably  occasioned  partly  by  putrefaction  and 
the  resulting  formation  of  gases,  the  germs  being  thrown  into 
the  air  by  bursting  gas  bubbles;  although  splashing  is  prob- 
ably the  more  common  cause  of  this. 

To  prevent  air  from  the  sewer  from  entering  houses 
two  general  methods  are  in  use:  placing  barriers  in  the 
house-connection  or  plumbing,  and  removing  the  sewer- 
air  through  other  outlets.  The  former  is  one  of  the  aims 
of  the  plumber  and  is  usually  attempted  by  the  use 


82  SEWERAGE. 

of  traps  The  latter  is  effected  by  natural  ventilation 
by  the  use  of  many  ventilating  devices,  in  few  or  none  of 
which  has  positive  action  been  successfully  obtained.  A 
combination  of  these  two  methods  gives  reasonably  good 
results  in  most  cases,  a  partial  obstruction  to  the  air  being 
placed  in  the  house-connection  or  its  branches  in  the  shape 
of  water-sealed  traps,  and  the  power  of  the  air  to  force  its 
way  through  these  being  lessened  by  ventilation. 

If  the  sewer  were  a  tight  conduit  with  no  inlets  or  outlets 
except  through  the  house-connections  and  the  main  outlet 
the  sewer-air  must  remain  constantly  unchanged  and  stagnant, 
or  must  find  exit  and  entrance  through  these  house-connec- 
tions. The  first  condition  is  impossible,  for  the  amount  of 
sewage  varies  from  hour  to  hour  and  must  displace  and  in  turn 
be  displaced  by  air  driven  to  and  derived  from  some  outside 
source.  In  case  of  a  sudden  discharge  of  sewage  into  such  a 
sewer  the  air  will  be  driven  through  the  only  outlets — the 
house-connections — unsealing  the  main  traps,  and  the  second- 
ary ones  also  unless  these  be  amply  vented.  A  strong  wind 
blowing  up  the  sewer  from  the  outlet  may  produce  the  same 
result.  In  addition  to  ventilating  the  sewer  it  is  therefore 
advisable  to  insure  a  continuously  free  air  outlet  to  every 
soil  pipe. 

Attempts  have  been  made  to  constantly  remove  the  air 
from  sewers  by  either  sucking  out  the  foul  air  or  forcing  in 
fresh;  that  is,  by  producing  a  current  through  the  sewer  to  a 
given  outlet  by  either  the  vacuum  or  plenum  process.  Both 
have  proved  failures  as  well  as  very  expensive.  In  no  experi- 
mental case  has  the  effect  been  felt  more  than  1000  feet  from 
the  fans  or  other  apparatus,  not  only  on  account  of  the  great 
amount  of  air  in  the  sewer-mains  and  laterals  to  be  moved, 
but  because  the  traps  in  the  house-connections  were  unsealed 
by  the  pressure  and  air  sucked  from  or  forced  into  the 
buildings,  according  to  the  system  employed. 

The  Metropolitan  Board  of  Works,  London,  concluded. 


.         °F  THE 
UNIVERSITY 

Of " 

...   - 

FLUSHING   AND    VENTILATION.  83 

after  exhaustive  study  of  the  question,  "  that  the  method  of 
ventilation  adopted  in  mines,  where  there  are  only  two  open- 
ings to  be  dealt  with  (an  inlet  for  the  air  at  one  end  and  an 

o  v 

outlet  for  it  at  the  other),  is  inapplicable  to  sewers."  This 
characteristic  of  a  sewerage  system  renders  impracticable  all 
methods  of  ventilation  depending  upon  one  or  two  ventilators 
to  each  line  of  sewers:  such  as  connecting  the  sewer-end  with 
a  chimney,  which  would  afford  little  more  ventilation  than  an 
untrapped  soil-pipe  at  the  same  point  or  a  special  ventilating- 
manhole. 

Many  expedients  for  ventilation  have  been  devised  and 
tried — among  them  connecting  the  sewers  to  street-lamps, 
where  a  suction  is  caused  and  the  gas  burned  by  a  constant 
flame;  placing  in  the  crown  of  brick  sewers  small  perforated 
pipes  connected  with  "  uptake-shafts,"  expected  to  cause  a 
continuous  removal  of  the  gases;  leading  pipes  from  the 
sewer  to  special  flues  constructed  in  houses,  within  the  body 
of  the  walls,  adjacent  to  the  chimney,  or  upon  the  outside  of 
the  house  and  running  up  above  all  windows;  leaving  the 
main  house-drains  untrapped  and  extending  them  above  the 
roofs;  placing  flap-doors  in  the  sewers,  opening  downward  for 
the  sewage,  but  closed  to  air,  which  can  escape  through  open- 
ings just  above  such  flaps;  placing  in  the  street  centre  at 
intervals  along  the  sewer  manholes  or  other  ventilating-shafts 
with  perforated  covers;  connecting  the  sewers  by  untrapped 
pipes  with  street-inlets  at  the  curb  line.  In  connection  with 
these,  charcoal  and  other  deodorizers  are  sometimes  placed  at 
the  air-outlets. 

There  seems  to  be  evidence  in  favor  of  the  conclusion  that 
the  greatest  danger  exists  in  the  house-connections  themselves 
and  not  in  the  sewers,  although  the  latter  should  be  prevented 
from  contributing  to  this  danger.  Of  many  analyses  of  sewer- 
air  made  not  one  to  the  author's  knowledge  has  shown  a 


84  SEWERAGE. 

greater  impurity  than  that  in  a  crowded  city  street,  whether 
CO,,  oxygen,  or  bacteria  be  taken  as  the  basis  of  comparison. 
Equally  positive  proof  goes  to  show  that  the  average  house- 
connection  or  the  adjacent  soil  near  open  joints  in  the  same 
does  give  rise  to  dangerous  gases.  (It  is  probable  that  the 
upper  ends  of  branch  sewers,  if  not  flushed  well  and  often,  are 
open  to  the  same  charge.)  However,  a  rush  of  comparatively 
pure  air  from  the  sewer  forced  through  the  traps  of  a  foul 
house-connection  is  as  objectionable  as  though  it  itself  were 
polluted,  since  it  forces  into  the  building  the  impure  air  exist- 
ing in  such  connection.  Air  outlets  to  house  plumbing  should 
hence  be  of  such  capacity  and  so  placed  as  to  give  full  and  imme- 
diate passage  to  all  the  air  necessary  to  prevent  forcing  or  siphoning 
of  traps. 

This  fact,  that  the  house-connections  themselves  are  fully 
as  foul  as,  if  not  more  so  than,  the  sewers  should  be  more 
generally  recognized  and  better  provision  made  for  ventilating 
them.  This  is  reasonably  well  done  by  placing  a  vent-shaft 
just  above  the  main  trap,  continuing  the  soil-pipe  above  thej 
roof  and  venting  each  trap  throughout  the  house.  But  a  still] 
better  circulation  of  air  is  obtained  by  omitting  the  main  trap 
altogether  and  permitting  the  air  from  the  sewer  to  pass 
through  the  house-connection  unobstructed.  The  danger  of 
this  air  passing  the  traps  on  house-fixtures  is  no  greater  than 
that  of  the  soil-pipe  air  doing  the  same,  and  in  the  majority 
of  cases  the  sewer  air  is  the  less  dangerous.  Such  construc- 
tion is  also  of  great  assistance  in  ventilating  the  sewer.  If 
only  an  occasional  house-connection  be  left  untrapped,  how- 
ever, the  odors  from  this  may  be  objectionable,  the  sewer  air 
being  but  little  diluted  by  the  infrequent  openings.  But  the 
author  knows  of  no  city  which  makes  this  method  compul- 
sory in  all  connections  where  it  is  not  perfectly  satisfactory. 


FLUSHING  AND    VENTILATION.  85 

The  use  of  street-lamps  as  outlets  may  sometimes  be  advan- 
tageous, but  in  this  country  the  cities  which  have  tried  it  have 
not  found  it  of  much  value.  The  use  of  hollow  electric-light  poles 
was  tried  in  Columbus,  O.,  in  1898,  but  was  not  found  to  be  worth 
adopting.  The  general  use  of  flap-doors  in  the  sewers  presup- 
poses a  regular  flow  of  air  in  a  fixed  direction  through  the  sewer, 
which  investigation  has  found  does  not  ordinarily  exist;  but  this 
use  may  be  advantageous  on  steep  grades,  where  there  is  a  tend- 
ency for  the  air  to  rise  past  intermediate  ventilating-^oints  to  the 
highest  ones.  Ventilation  through  manholes  and  other  ventilating- 
shafts  most,  if  not  all,  engineers  recommend,  although  many  do 
not  consider  these  sufficient. 

The  use  of  storm-water  inlets  for  this  purpose  is  much  op- 
posed by  many,  who  contend  that  the  sewer-air  should  not  be 
discharged  so  near  to  passers-by  upon  the  sidewalk.  In  fact 
this  same  argument  is  used  by  a  few  against  ventilation  through 
manholes  in  the  centre  of  the  street.  It  is  probable  that 
the  danger  from  this  cause  is  very  slight,  if  it  exists  at  all, 
since  it  is  dependent,  not  upon  the  gases,  which  are  enor- 
mously diluted  upon  reaching  the  outer  air,  but  upon  the 
presence  of  disease-germs  in  the  exhalations,  which  has  been 
disproven.  Moreover,  the  average  catch-basin,  even  if  just 
cleaned  (as  this  cleaning  is  ordinarily  done),  is  more  offensive 
than  any  rightly  designed  sewer  is  at  all  likely  to  become;  and 
it  is  extremely  doubtful  if,  in  connection  with  its  odors,  any 
contribution  of  air  from  the  sewer  could  be  detected.  For 
these  reasons  it  seems  to  the  author  desirable  to  connect  the 
sewer  with  the  street-inlets  by  ventilating-pipes  and  to  place 
manholes  with  perforated  heads  at  intervals.  Since  the 
latter  are  apt  to  be  sealed  in  winter  by  ice  and  snow,  and  in 
summer  by  mud,  the  additional  ventilation  through  the  street- 
inlets  would  seem  to  be  advisable,  particularly  if  the  sewer  be 


86  SEWERAGE. 

not  ventilated  through  the  house-drains.  A  small  amount  of 
snow  will  not  ordinarily  stop  the  openings  in  a  manhole-cover, 
owing  to  the  warm  air  of  the  sewer,  but  a  heavy  storm  or 
frozen  mud  may  easily  do  so. 

Since  the  proportion  of  air  iu  a  small  sewer  to  the  dis- 
charge into  the  same  is  much  less  than  in  the  case  of  a  large 
combined  sewer,  and  consequently  the  effect  of  a  given  dis- 
charge is  a  greater  compression  of,  and  pressure  transmitted 
by,  the  air  in  the  smaller  sewer,  the  sewers  of  the  separate 
system  need  ventilation  or  safety-vents  even  more  than  do 
those  of  the  combined.  In  case  there  are  storm-water  inlets 
to  which  ventilation-pipes  from  house-sewers  may  be  led  this 
method  may  be  adopted;  but  ventilation  through  untrapped 
house-connections  is  probably  more  efficient.  This  extra 
ventilation  is  very  often — perhaps  in  the  majority  of  cases — 
neglected,  but  such  omission  is  undoubtedly  attended  with 
danger. 

For  house-sewers,  ventilating  manhole-heads  and  un- 
trapped house-drains;  for  combined  sewers,  these  with  the 
addition  of  untrapped  street-inlets;  and  for  storm-sewers, 
manholes  and  inlets — these,  with  flap-doors  on  steep  grades, 
seem  to  the  author  the  best  methods  so  far  devised  for  ven- 
tilation ;  and  without  ventilation  any  system  will  almost  surely 
become  a  nuisance  and  a  danger.  The  aim  should  be  to  se- 
cure by  whatever  method  the  greatest  possible  number  and 
freedom  of  communications  between  the  sewer  and  the  outer 
air;  and  there  is  little  doubt  but  that  when  this  is  realized 
the  sewer  air  becomes  so  diluted  and  the  organic  matter  float- 
ing in  it  so  oxidized  as  to  render  it  less  dangerous  and  objec- 
tionable than  the  air  of  a  crowded  church  or  theatre.  When 
this  is  not  true  the  sewers  are  probably  in  great  need  of  clean- 
ing and  flushing. 

V 


CHAPTER  V. 
COLLECTING  THE  DATA. 

ART.  25.     DATA  REQUIRED. 

ANY  ptans  made  before  the  full  and  complete  data  are  at 
hand  may  be  shown  by  further  information  to  be  inadvisable, 
while  their  very  existence  may  create  a  prejudice  against  the 
substitution  of  more  efficacious  ones.  Therefore,  although 
the  development  of  the  plans  may  suggest  the  desirability  of 
further  data  the  necessity  for  which  was  unforeseen,  as  much 
as  seems  necessary  in  this  line  and  that  of  surveys  should  be 
done  preliminary  to  any  designing. 

The  first  necessity  will  be  for  a  map  of  the  district  under 
consideration.  This  will  usually  include  the  city  or  town 
and  all  land  over  which  it  may  spread  in  the  future;  also  all 
adjacent  areas  which  shed  their  water  into  or  across  the  sur- 
face of  this  territory.  This  map  should  show  all  streets,  lanes, 
etc. ;  all  parks  or  other  areas  permanently  devoted  to  vegeta- 
tion; all  rivers,  creeks,  ponds,  or  other  bodies  of  water — in 
fact  all  natural  and  artificial  divisions  of  the  area  embraced  by 
the  corporate  limits.  It  usually  happens  that  this  much  can 
be  found  already  mapped  for  other  purposes;  but  unless  it  is 
known  that  the  measurements  from  which  such  map  was  pre- 
pared were  accurately  taken  a  sufficient  number  of  check 
measurements  should  be  made  to  establish  its  accuracy  or  the 
reverse.  On  the  point  of  accuracy  a  question  may  arise  as  to 
how  exactly  the  measurements  should  be  taken.  If  these 

87 


88  SEWERAGE. 

should  involve  an  error  of  no  more  than  .2%  they  would  be 
sufficiently  accurate  for  the  work  in  hand.  For,  as  sewer 
grades  are  ordinarily  run  from  manhole  to  manhole,  and  these 
are  about  300  feet  apart,  an  error  of  .2$  would  mean  that  of 
.6  foot  in  that  distance,  which  on  a  grade  of  .5^  (a  fairly 
steep  one)  would  involve  an  error  in  grade  of  .003  foot,  which 
is  much  less  than  the  least  which  could  be  expected  in  the 
construction  of  the  sewer. 

It  will  be  advisable  to  obtain  also  the  location  of  all  street- 
railroads,  and  of  all  gas-  and  water-pipes,  their  distance  from 
the  curb  or  side  lines  of  the  street  and  the  depth  of  the 
pipes  being  noted.  Also  the  location,  grade,  size,  and  con- 
dition of  any  existing  sewers  and  appurtenances  should  be 
ascertained,  by  actual  inspection  if  possible. 

The  data  for  computing  the  extent  of  tributary  drainage- 
areas  will  ordinarily  need  to  be  collected  in  their  entirety,  as 
it  is  seldom  that  such  information  exists  in  a  serviceable  form. 
The  topographical  surveys  which  have  been  made  of  several 
of  the  States,  however,  may  be  used  to  great  advantage  in 
this  connection.  The  data  desired  include  the  boundaries 
of  the  watersheds  whose  run-off  does  not  reach  a  confined 
channel  before  entering  the  limits  of  the  territory  to  be 
sewered.  (Such  water  as  passes  through  this  territory  in  the 
form  of  streams  rather  than  flowing  over  the  ground  does  not 
affect  the  problem,  unless  these  streams  are  to  be  walled  in, 
in  which  case  each  one  will  form  a  problem  by  itself.)  Also 
the  slope  of  the  ground  and  the  character  of  the  soil  as  to 
permeability  should  be  ascertained,  the  location  and  extent 
of  rock  at  or  near  the  surface,  of  woods  and  of  orchards. 
Care  should  be  taken  to  note  and  locate  any  slightly  worn 
channels  along  which  storm-water  ordinarily  flows  to  the 
nearest  creek  or  rivulet  across  territory  not  yet  built  up,  as 
these,  if  they  cross  into  the  sewer  district,  indicate  the  points 
at  which  the  storm-water  must  be  intercepted. 


COLLECTING    THE   DATA.  89 

Such  levels  must  be  taken  as  are  necessary  for  the  plot- 
ting of  profiles  of  each  street,  alley,  or  any  other  surface  under 
which  a  sewer  is  to  run,  including  a  profile  across  the  bed  of 
each  stream  crossed,  with  the  elevation  of  high-  and  low-water 
marks;  also  the  elevation  of  the  body  of  water  into  which 
either  the  crude  or  purified  sewage  is  to  be  discharged,  the 
elevation  during  drought  and  flood  as  well  as  the  ordinary 
elevation  being  ascertained.  The  depths  must  be  obtained 
of  all  cellars  whose  bottoms  are  not  evidently  above  the  grade 
of  the  proposed  sewer,  unless  all  sewers  are  to  be  placed  at  a 
fixed  minimum  depth,  which  is  to  be  increased  only  by  the 
demands  of  the  necessary  sewer  grades  and  not  by  the  depth 
of  any  cellar  or  basement  (see  Art.  37).  Also  if  grades  have 
been  adopted  for  any  street,  but  not  yet  carried  into  effect, 
these  as  well  as  the  existing  surfaces  should  be  obtained. 

If  a  disposal-ground  is  to  be  used  for  filtration  or  irriga- 
tion a  careful  levelling  of  its  entire  surface  must  be  made, 
and  test-pits  sunk  to  ascertain  the  character  of  the  material 
to  a  depth  of  5  to  8  feet. 

If  it  is  considered  desirable  to  discharge  the  crude  sewage 
into  a  given  body  of  fresh  or  salt  water  careful  search  should 
be  made  for  the  point  best  suited  for  the  outlet;  also  in  case 
of  a  river  whether  the  dilution  afforded  in  time  of  drought 
will  be  sufficient  to  prevent  a  nuisance.  For  this  purpose  the 
action  of  currents,  tides,  and  prevailing  winds  should  be 
investigated.  Gaugings  of  the  discharge  of  streams  should 
be  made,  and  inquiry  as  to  whether  and  at  what  points  further 
down  the  river  the  water  is  used  for  a  public  supply.  It  is 
well  also  to  have  analyses  made  of  river-water  taken  at  inter- 
vals below  the  proposed  outlet  for  use  in  possible  suits  against 
the  city  for  nuisance ;  this  whether  or  not  the  sewage  is  to 
be  treated. 

The  engineer  should  in  person  pass  through  every  street 
in  the  district  to  be  sewered,  noting  the  character  of  each,  the 


90  SE  WERA  GE. 

location  of  the  business  and  factory  districts,  the  general 
character  of  the  pavements  and  yards,  and  the  average  size  of 
lot  occupied  by  each  residence.  He  must  also  ascertain  as 
nearly  as  may  be  the  present  population  and  its  past  rate  of 
increase;  the  probable  direction  and  extent  of  the  future 
growth  of  the  business  part  of  the  city,  as  well  as  of  the  city 
as  a  whole.  He  should  obtain  the  figures,  if  they  exist,  of 
water-consumption  in  this  and  neighboring  cities;  also  all 
possible  data  concerning  the  rainfall. 

A  considerable  amount  of  other  information  will  in  many 
instances  be  desirable,  called  for  by  the  peculiarities  of  each 
case.  Many  items,  such  as  cost  of  materials  and  labor  (for 
use  in  the  estimate),  will  suggest  themselves  as  they  are 
needed. 

ART.  26.     SURVEYING  AND  PLOTTING. 

Since  extreme  accuracy  is  not  necessary  in  the  transit 
survey,  the  use  of  the  ordinary  stadia  methods  will  be  found 
advantageous  for  either  check  or  original  surveys.  Stadia- 
hairs  in  the  level,  for  use  in  running  street-profiles,  will  be 
found  to  expedite  this  work,  and  will  permit  reducing  the 
number  in  the  level  party  to  two.  The  adjustment  of  the 
stadia-hairs  should  be  frequently  checked. 

The  tributary  drainage-areas  will  not  need  to  be  surveyed 
in  great  detail.  If  the  natural  features  are  boldly  accentuated 
it  may  be  sufficient  to  locate  by  a  transit-line  the  limiting 
summits  and  ridges,  both  main  ridges  and  spurs.  If  the 
country  is  gently  rolling  or  generally  flat  contour  surveys 
should  be  made  of  the  whole  drainage-area,  or  at  least  of  any 
portion  of  it  the  disposal  of  whose  run-off  may  offer  difficul- 
ties. 

Of  such  undeveloped  areas  as  may  be  reached  by  the  city 
in  its  future  growth  and  which  will  be  embraced  in  drainage- 
areas  for  which  sewers  are  to  be  at  once  designed  accurate 


COLLECTING    THE  DATA.  pi 

contour  surveys  should  be  made,  contours  being  located  from 
I  to  25  feet  apart  vertically,  according  to  the  nature  of  the 
country.  They  should  be  sufficiently  close  to  show  the  con- 
figuration of  the  ground  in  considerable  detail,  but  not  so  close 
that  the  contour-lines  will  obscure  all  else  upon  the  map. 

Most  cities  and  towns  of  any  size  have  the  street  grades 
established  and  recorded  with  their  profiles.  An  extensive 
experience  in  attempts  at  the  adaptation  of  such  information 
to  the  requirements  of  sewer-designing  has  demonstrated  that 
in  nine  cases  out  of  ten  it  is  waste  of  time  to  attempt  to  use 
these  records  and  profiles.  For  the  levels  have  usually  been 
taken  by  a  succession  of  surveyors  of  varying  degrees  of 
efficiency;  occasionally  also  the  grades  have  been  altered  on 
the  ground,  but  not  upon  the  profile;  and  the  time  employed 
in  discovering  and  rectifying  errors  and  omissions  would 
generally  have  sufficed  for  taking  entirely  new  levels. 

The  levels  of  the  street-surfaces  taken  for  the  profile 
need  be  to  tenths  of  a  foot  only,  but  the  bench-marks  and 
back-  and  fore-sights  should  be  to  thousandths.  Readings 
should  be  taken  along  each  proposed  sewer-line  not  more  than 
100  feet  apart,  at  every  pronounced  change  of  grade  and  at 
street  intersections;  the  elevation  of  rails  where  the  line 
crosses  a  railway,  and  at  stream-crossings  the  profile  of  the 
bottom  and  the  water-surface,  should  be  obtained. 

A  convenient  scale  for  a  map  of  a  village  or  borough  is 
200  feet  to  I  inch,  but  if  its  size  is  such  that  this  scale  would 
necessitate  the  use  of  paper  more  than  3  feet  wide  it  may  be 
better  to  use  a  scale  of  250  or  300  feet  to  I  inch.  It  is  inad- 
visable to  use  a  smaller  scale  than  this,  and  if  the  resulting 
map  is  still  too  large  for  the  paper  it  may  be  necessary  to 
spread  it  over  two  or  more  sheets.  In  such  a  case  it  will  be 
found  convenient,  where  conditions  permit  of  it,  to  so  arrange 
the  sheets  that  each  drainage-area  shall  appear  upon  one  sheet 
only.  Upon  this  map  should  be  shown  the  location  of 


92  SEWERAGE. 

the  proposed  sewers  and  all  appurtenances,  these  being 
usually  in  red. 

A  convenient  scale  for  the  profiles  is  25  feet  to  I  inch 
horizontal  and  5  feet  to  I  inch  vertical.  These  should  show 
the  sewer-line  at  its  proper  grade,  the  depth  of  all  unusually 
low  cellars,  the  location  of  all  manholes  and  other  appurte- 
nances. A  plan  of  the  street  is  usually  placed  under  the 
profile,  showing  the  location  therein  of  the  sewer-line  and  all 
appurtenances. 

For  ascertaining  the  best  location  for  an  outlet  into  tidal 
waters  the  use  of  floats  is  desirable,  since  thus  can  be  learned 
the  ordinary  periodic  movements  of  the  water  into  which  the 
sewage  is  to  be  discharged,  and  hence  the  possibility  of  the 
creation  of  a  nuisance  thereby.  These  floats  should  expose 
as  little  surface  to  the  wind  as  possible.  A  pine  rod  or  tin 
tube,  weighted  at  the  botom  and  with  a  numbered  flag 
fastened  to  the  top,  is  usually  employed.  They  should  be 
started  at  different  stages  of  the  tide  from  each  point  which 
is  being  considered  as  a  possible  outlet.  Account  should  be 
kept  of  and  allowance  made  for  winds  during  the  times  the 
floats  are  in  the  water.  Each  float  should  be  numbered  and 
a  record  kept  showing  the  time  and  place  at  which  it  was  put 
into  the  water,  the  state  of  the  tide,  wind,  etc.  By  means 
of  one  or  more  boats  they  should  be  so  traced  that  the  path 
of  each  can  be  plotted  upon  a  map  until  it  strands  or  passes 
beyond  the  point  where  sewage  can  create  a  nuisance.  It 
may  at  times  be  necessary  to  follow  a  set  of  floats  night 
and  day  for  three  or  four  days;  seldom  longer  than  this,  for 
if  they  have  not  in  that  time  passed  to  a  considerable  distance 
from  the  starting-point  such  point  is  not  suitable  for  an 
outlet. 

The  quantity  of  water  flowing  in  a  given  stream  and  the 
resulting  dilution  can  be  ascertained  by  the  use  of  floats  or  a 
current-meter,  the  cross-section  of  the  stream  being  first 


COLLECTING    THE   DATA. 


obtained.  In  some  cases  this  flow  can  be  obtained  from  gaug- 
ings  by  the  U.  S.  Geological  Survey.  If  possible  a  gauging  of 
the  stream  during  a  drought  should  be  obtained,  since  it  is  even 
more  important  that  there  be  the  necessary  dilution  at  such  a 
time  than  when  the  river  is  high. 

It  is  sometimes  desirable  to  sink  test-pits  or  bore  at  inter- 
vals along  the  line  of  each  proposed  sewer  to  ascertain  the 
character  of  the  material  to  be  excavated.  This  is  unneces- 
sary where  cellars  or  other  excavations 
along  the  street-line  have  been  sunk  to 
practically  the  depth  of  the  sewer,  and 
when  neither  rock  nor  quicksand  is 
anticipated  it  is  seldom  of  a  service 
commensurate  with  the  cost.  In  sound- 


I 


Grip  for  raising  pipe 


FIG.  3.— SOUNDING-ROD.  FIG.  30.— SOUNDING-MACHINE. 

ing  for  rock  several  methods  have  been  used.  An  iron  rod, 
upset  and  pointed  at  one  end,  may  be  driven  to  a  depth  of  10  or 
12  feet  through  most  soils,  and  may  be  raised  again  by  a  handle, 
as  shown  in  Fig.  3,  which  can  if  necessary  be  fastened  to  a 
lever,  a  stout  wooden  horse  being  used  as  a  fulcrum.  It  is 
possible  to  reach  still  further  by  replacing  the  first  heavy  rod  by 
a  thinner  and  longer  one  driven  in  the  same  way. 

A  somewhat  more  elaborate  apparatus  is  shown  in  Fig.  30, 
which  has  been  driven  to  18  feet   in    sand   and  10  to  15  feet  in 


94  SEWERAGE. 

stiff  clay.  In  the  latter  soil  the  rod  should  be  turned  frequently 
with  Stillson  wrenches.  Care  should  be  taken  that  boulders  are 
not  mistaken  for  rock. 

When  there  are  not  many  boulders  or  gravel-stones  in  the 
soil  an  iron  pipe  about  i  inch  in  diameter  may  be  connected 
by  hose  with  a  fire-hydrant  and  sunk  into  the  ground  by  the 
"jet  process"  to  a  considerable  depth.  By  connecting  the 
hose  to  the  side  of  a  T  screwed  to  the  end  of  the  pipe  and 
capping  the  top  of  this  the  pipe  can  in  most  cases  be  driven 
by  hammer  past  any  small  stones  or  other  hard  obstacles. 

A  modified  post-hole  augur  can  be  used  for  the  same  pur- 
pose, with  the  advantage  that  by  it  samples  of  the  soils  passed 
through  may  be  obtained. 

For  deep  borings,  as  where  tunnelling  may  be  necessary, 
a  more  elaborate  outfit  is  used,  comprising  derrick  and  wind- 
ing drum  for  handling  pipe  for  wash  boring.  When  depth 
and  nature  of  rock  must  be  known  a  core  may  be  obtained 
by  diamond  drill. 

The  only  certain  method  of  detecting  the  presence  of  run- 
ning sand  is  by  sinking  a  test-pit,  though  the  absence  of  sand 
from  the  materials  removed  by  other  methods  would  of 
course  be  proof  of  its  absence.  The  washings  from  a  jet-pipe 
may  be  caught  and  from  the  sediment  some  idea  be  had  of 
the  materials  encountered,  though  not  of  their  consistency. 

The  presence  of  ground-water  in  any  quantity  is  fully  as 
important  a  matter  in  designing  as  the  presence  of  rock,  and 
should  be  thoroughly  investigated.  Ground-water  is  fre- 
quently found  in  porous  soils  just  at  the  base  of  a  hill.  It  is 
usually  found  in  gravelly  soils,  near  hills  or  mountain 
streams  whose  waters  percolate  into  the  porous  ground. 
Usually  (although  there  are  exceptions)  but  little  water 
reaches  the  soil  from  rivers,  whose  beds  are  in  most  cases  im- 
pervious. The  presence  and  amount  of  ground-water  can  be 
known  only  by  excavating  or  from  existing  wells. 


CHAPTER   VI. 
THE   DESIGN, 

No  general  directions  for  designing  a  sewerage  system  can 
be  given  which  will  cover  all  the  conditions  met  with  in  every 
case.  But  upon  the  principles  already  stated  may  be  based  any 
special  designs,  care  being  taken  to  violate  none  of  the 
requirements  of  sanitary  sewerage.  In  many  cases  no  emer- 
gency will  arise  out  of  the  ordinary.  To  such  the  methods 
herein  outlined  apply,  but  even  in  the  use  of  these  skill  and 
judgment  must  be  employed,  and  it  may  frequently  be  neces- 
sary, as  it  is  always  desirable,  to  call  upon  the  services  of  an 
experienced  consulting  engineer  for  a  decision  as  to  some  of 
the  vital  principles  involved  in  the  design;  such,  for  instance, 
as  the  system  to  be  employed  and  the  method  of  disposal. 
But  many  small  cities  and  towns  cannot  afford  this  expense — 
or  think  they  cannot — and  the  city  engineer  must  rely  wholly 
upon  himself  for  the  design  as  a  whole  and  in  detail.  It  is 
hoped  that  the  principles  already  stated  and  the  methods  fol- 
lowing may  be  of  service  to  him. 

ART.  27.     GENERAL  PRINCIPLES. 

The  first  matter  to  be  decided  upon  in  preparing  the  design 
is,  How  much  and  what  kind  of  sewage  must  be  provided  for? 
the  second,  What  disposal  shall  be  made  of  it?  the  third, 
What  system — separate,  combined,  or  compound — shall  be 
employed  ? 

95 


96  SEWEXAGE. 

It  is  assumed  that  all  urban  districts  require  house-sewer- 
age. Local  circumstances,  financial,  topographical,  and  geo- 
graphical, will  usually  decide  whether  or  not  storm-water  also 
shall  be  removed  by  the  sewers.  In  small  cities  there  are 
usually  a  few  places  the  removal  of  storm-water  from  which  is 
almost  imperative.  These  places  must  be  ascertained,  the 
area  draining  to  them  measured  on  the  contour-map,  and  an 
estimate  made  of  the  run-off  based  upon  the  principles  given 
in  Articles  18-20. 

In  towns  or  districts  which  are  closely  built  up  the  storm- 
water  should  not  flow  in  the  gutters  more  than  two  blocks — 
or  say  700  feet — before  finding  a  sewer-inlet  or  some  natural 
stream  or  channel  into  which  it  can  discharge.  In  residence 
or  suburban  districts  the  same  rule  applies  when  the  streets 
have  impervious  pavements  and  the  yards  are  small.  As  the 
pavements  become  more  pervious  and  the  houses  more  scat- 
tered this  distance  can  be  considerably  increased  and  the 
extent  of  the  storm-sewer  system  proportionately  reduced. 
The  judgment  as  to  how  many  localities  (from  a  lack  of  water- 
courses or  other  reasons)  need  storm-sewers  must  be  balanced 
against  the  funds  available  for  such  sewers.  If  possible,  how- 
ever, the  storm-sewers  should  serve  as  wide  a  territory  as  the 
house-sewerage  system. 

In  most  small  cities  natural  watercourses  are  retained  to 
carry  away  the  run-off,  and  the  service  rendered  by  these 
may  be  made  adequate — if  it  is  not  already  so — by  enlarging, 
straightening,  and  walling  them.  (If  the  money  necessary  for 
substituting  a  storm-sewer  for  such  a  drain  is  available  this 
should  of  course  be  done.)  The  residents  along  such  a  water- 
course should  be  prohibited  from  depositing  any  excreta, 
garbage,  or  other  refuse  therein ;  and  if  this  is  enforced  and 
the  stream  so  enlarged  as  to  prevent  overflowing  it  will 
become  a  good  substitute  for  a  storm-sewer,  and  much  less 
objectionable  than  such  small  streams  ordinarily  are  to  the 


THE   DESIGN.  97 

occupants  of  the  property  it  traverses.      For  the  amount  of 
water  to  be  provided  for  from  given  areas  see  Arts.  12-14. 

A  short  summary  of  some  of  the  principles  previously 
stated  may  be  given  here  to  advantage,  with  applications  of 
the  same. 

The  amount  of  house-sewage  depends,  first,  upon  the 
population  to  be  provided  for.  This  must  be  the  population 
some  years  in  the  future;  some  say  30,  some  50  years.  The 
first  seems  preferable  in  most  cases,  since  the  larger  sewers 
called  for  by  the  second  will  be  less  suited  to  the  needs  of  the 
present,  deposits  dangerous  to  health  more  probable,  and 
consequently  cost  of  maintenance  greater;  alsq  in  most  cases 
the  difference  in  cost  at  compound  interest  for  30  years  would 
amount  to  sufficient  at  the  end  of  that  time  to  build  a  system 
adequate  for  the  increased  needs.  Moreover,  the  growth  can- 
not be  predicted  with  any  great  accuracy  30,  and  still  less  50, 
years  ahead.  From  the  estimate  of  Baltimore's  growth  made 
by  the  Sewerage  Commission  it  is  calculated  that  to  pro- 
vide for  a  population  for  30  years  ahead  would  call  for  sewer- 
mains  of  twice  the  capacity  at  present  required ;  while  if  that 
for  50  years  ahead  were  adopted  as  the  number  to  be  provided 
for  the  mains  would  need  to  be  more  than  three  times  such 
capacity. 

For  making  this  prediction  it  is  customary  to  plot  all 
known  past  populations,  each  year  and  its  corresponding 
population  being  made  coordinates  of  as  many  points.  A 
curve  is  passed  as  nearly  through  these  points  as  possible,  and 
with  the  same  law  of  curvature  is  continued  ahead  far  enough 
to  cover  the  time  required.  It  is  evident  that  such  a  curve 
should  not  return  on  itself  horizontally,  but  must  approach 
an  asymptote  whose  direction  the  judgment  must  decide;  or 
the  curve  may  in  reality  even  reverse.  This  method  is  but  a 
"  scientific  guess,"  but  there  seems  to  be  no  better  one.  As 
a  general  rule  the  smaller  the  city  or  town  the  greater  the 


98  SEWERAGE. 

probability  of  sudden  and  great  unforeseen  changes  in  the  rate 
of  growth. 

The  estimate  of  per  capita  water-consumption  is  similarly 
difficult.  There  is  no  necessity  for  this  exceeding  50  or  60 
gallons  daily,  and  yet  it  may  reach  200  or  even  300  for  any- 
thing which  we  know  to  the  contrary.  Since  it  can  be  con- 
fined well  within  the  100  mark  by  the  use  of  meters  and 
thorough  inspection,  it  seems  wasteful  of  capacity  and  capital 
to  provide  for  more.  The  probability  is  that  the  near  future 
will  see  the  consumption  almost  universally  reduced  below 
this  limit. 

The  population  decided  upon  times  the  per  capita  water- 
consumption  and  plus  the  leakage  may  be  taken  as  the 
amount  of  sewage  to  be  provided  for. 

The  character  of  the  sewage,  involving  the  proportionate 
amount  of  house-wastes  and  diluting-water,  the  character  of 
the  water  supplied,  the  presence  of  acids  or  other  manufac- 
turing wastes,  will  have  a  bearing  upon  the  method  of  dis- 
posal. 

In  deciding  upon  the  disposal  to  be  adopted,  if  that  by 
dilution  is  practicable  the  laws  of  the  State  should  be  investi- 
gated to  determine  its  legality;  the  direction  and  velocity  of 
tides  and  currents  should  be  known  to  be  such  as  to  remove 
the  sewage  continuously  from  rather  than  toward  all  shores 
or  other  places  where  it  may  be  deposited  and  create  a 
nuisance;  the  number  of  gallons  of  unpolluted  water  passing 
the  outlet  each  day  should  be  equivalent  to  at  least  1500 
times  the  population;  the  velocity  of  the  water  past  the  out- 
let must  be  sufficient  to  prevent  the  deposit  of  sewage  matter 
at  or  near  said  outlet.  The  effect  of  the  discharge  upon 
bathing-beaches,  upon  fish,  oysters,  or  other  food  matter, 
upon  the  water-supply  of  towns  below,  or  upon  manufactur- 
ing interests — these  must  all  be  studied,  both  on  their  scien- 
tific and  commercial  sides. 


THE   DESIGN.  99 

If  from  these  investigations  dilution  is  found  inadvisable 
the  method  of  treatment  best  adapted  to  the  circumstances 
must  be  sought.  Search  should  be  made  for  a  spot  or 
spots  which  are  low  and  flat,  but  not  boggy,  whose  soil  is 
pervious  and  whose  value  is  low  (although  land  which  pos- 
sesses none  of  these  qualities  can  be  used  for  sewage  disposal), 
and  whose  extent  is  sufficient  for  years  to  come.  If  the 
sewage  must  be  thoroughly  purified  filtration  or  irrigation 
must  be  used,  alone  or  in  connection  with  some  preliminary 
treatment.  Chemical  precipitation  may  be  employed  alone 
where  a  removal  of  50%  to  65%  of  the  impurities  will  be  suffi- 
cient. (See  Chapters  XV,  XVI,  XVII,  and  XVIII  for  a  -dis- 
cussion of  this  subject,  which  should  be  carefully  studied 
before  deciding  upon  any  scheme  of  treatment.) 

It  will  usually  be  well  to  make  preliminary  plans  based 
upon  each  of  two  or  three  methods  of  disposal  and  compare 
them  from  both  sanitary  and  financial  points  of  view. 

A  decision  as  to  the  system  to  be  employed  should  ordi- 
narily rest  largely  upon  the  decisions  of  the  two  previous 
points.  If  treatment  of  the  sewage  is  necessary  or  will 
probably  become  so  in  the  course  of  20  or  30  years,  or  if  the 
house-sewage  is  to  be  discharged  at  some  distance  from  the 
centre  of  the  city,  the  separate  or  compound  system  will 
usually  be  advisable. 

If  there  are  a  number  of  convenient  points  along  a  water 
front  at  each  of  which  house-sewage  can  be  discharged  with- 
out nuisance  the  combined  system  may  be  the  cheapest  and 
most  desirable.  If  there  already  exist  large  sewers  discharg- 
ing at  various  points  where  the  discharge  of  house-sewage 
creates  a  nuisance,  or  of  a  character  not  adapted  to  carrying 
house-sewage  (because  of  flat  bottoms  or  rough  interior),  the 
separate  system  will  usually  be  advisable,  the  old  sewers 
being  used  in  the  storm-sewer  system.  If  such  large  sewers 
are  adapted  in  interior  surface  and  form  to  carrying  house- 


100  SEWERAGE. 

sewage,  however,  they  may  be  retained  for  this  purpose,  but 
an  intercepting  sewer  built  to  receive  from  them  the  dry- 
weather  flow  and  convey  it  to  a  suitable  outlet,  the  storm- 
water  discharging  through  the  previous  outlets. 

In  all  these  matters,  however,  engineering  experience  and 
judgment,  and  not  fixed  rules,  should  be  the  basis  of  decision. 

The  general  rule  in  sewerage,  as  in  other  engineering  work, 
is:  obtain  the  best  results  and  at  the  least  cost.  Certainty 
of  attaining  this  will  frequently  require  the  preparation  and 
comparison  of  alternative  plans,  both  of  the  system  as  a 
whole  and  of  its  separate  parts. 

ART.  28.     SUBDIVISION  INTO  DISTRICTS. 

For  the  purpose  of  sewerage-designing  the  territory  under 
consideration  is  ordinarily  divided  into  two  sets  of  districts, 
one  based  upon  the  density  of  population,  the  other  upon  the 
slope  of  the  ground-surface. 

The  former  division  should  take  as  a  basis  the  probable 
density  of  population  per  acre  of  different  sections  at  some 
time — say  30  years — in  the  future,  since  the  system  must 
serve  the  population  at  that  time  as  well  as  in  the  present. 
It  will  be  convenient  to  base  the  division  upon  population  per 
acre  of  20,  30,  and  other  factors  of  10,  20  being  the  minimum 
assumed  for  habitable  districts  in  most  cities.  The  maximum 
may  run  up  to  150  or  more  per  acre.  As  this  division  is  for 
the  purpose  of  design  only  and  is  not  usually  shown  upon  the 
finished  map,  it  may  be  designated  by  bounding-lines  or  by 
tints  upon  a  working  map.  (It  will  be  well  to  have  several 
copies — white  or  blue  prints  will  do — of  the  city  map  as  work- 
ing maps.)  Having  made  the  above  subdivision,  the  total 
population  of  each  area,  calculated  from  the  assumed  density 
of  population,  should  be  ascertained,  and  the  sum  of  all  these 
compared  with  the  future  total  population  as  estimated  by  use 


THE  DESIGN.  IOI 

of  the  curve  (Art.  27).  It  may  exceed  this  by  a  small 
amount — say  \Q% — to  allow  for  incorrect  apportioning  of 
densities.  If  it  does  not  at  least  equal  it  changes  in  the 
extent  of  the  different  areas  should  be  made  sufficient  to  give 
this  total  and  at  such  points  as  the  engineer's  best  judgment 
dictates. 

The  second  subdivision  is  that  into  drainage  districts. 
For  this  purpose  a  carefully  prepared  contour-map  of  the  city 
or  area  to  be  sewered  is  necessary.  Each  district  is  to  con> 
tain  all  the  territory  draining  into  one  main  sewer,  together 
with  that  main  down  to  its  outlet  or  junction  with  the  inter- 
cepting or  outlet  sewer.  Under  some  plans  of  sewer  assess- 
ments this  subdivision  is  necessary  for  other  than  engineering 
purposes.  For  house-sewers  it  can  usually  be  best  made 
after  the  designing  of  the  sewers  is  completed.  For  storm- 
sewers,  however,  it  should  be  made  after  the  lines  are  located, 
but  before  the  sizes  are  determined  upon,  to  facilitate  calcu- 
lation of  the  latter. 

ART.  29.     LOCATING  THE  SEWER-LINES. 

Unless  this  location  is  already  occupied  by  gas-  or  water- 
pipes  or  a  street-railroad,  house  and  combined  sewers  are  in 
most  cases  located  in  the  centres  of  streets  or  alleys,  the  cost 
to  the  householders  on  each  side  for  house-connections  being 
thus  made  equal.  In  some  cities  the  sewers  are  located  under 
the  sidewalks,  there  being  a  line  on  each  side  of  the  street. 
This  plan,  which  is  used  at  Washington,  D.  C.,  quite  exten- 
sively, is  usually  adopted  in  the  case  of  wide  streets,  since 
there  the  cost  of  the  extra  line  is  less  than  that  of  the  addi- 
tional lengths  of  house-connections  required  by  a  single  sewer. 
From  a  financial  standpoint  the  double  line  is  cheaper  when 
the  cost  of  a  minimum-sized  sewer  (6-  or  8-inch)  of  a  length 
equal  to  the  average  house-lot  frontage  is  less  than  the  cost 


102  SEWERAGE. 

of  a  house-connection  of  a  length  equal  to  the  distance 
between  the  two  sewer-lines.  Another  advantage  of  side 
sewers  is  that  the  street-paving  need  not  be  torn  up  in  making 
house-connections.  A  serious  disadvantage  is  that  the  dis- 
tance from  the  upper  end  of  each  line  to  the  point  where  the 
sewage  flow  is  self-cleansing  in  volume  and  velocity  will  be 
double  that  when  but  a  single  line  is  laid.  Also  the  roots  of 
shade-trees  are  apt  to  cause  serious  trouble  by  entering  the 
pipe-joints.  Probably  the  best  method  of  avoiding  both 
these  last  objections  and  that  of  the  continual  tearing  up  of 
the  street-pavement  is  to  lay  the  sewer  in  the  street  centre 
and  at  the  same  time  carry  each  house-connection  to  the  curb. 

Where  a  city  has  alleys  intermediate  between  the  streets 
it  may  sometimes  be  advisable  to  carry  the  sewers  through 
these  rather  than  through  the  streets,  the  principal  argument 
for  this  being  that  less  valuable  paving  is  destroyed  and  less 
obstruction  caused  to  traffic  by  the  work  of  construction. 
On  the  other  hand  the  house-connection  will  be  longer,  and 
both  the  cost  increased  and  the  grade  in  such  connection 
decreased,  if  the  distance  from  the  house  to  the  street  centre 
is  less  than  that  to  the  alley  centre,  as  is  generally  the  case. 
Moreover,  the  paving  in  an  alley  should  be  equally  as  good  as 
that  in  a  street,  and  the  unevenness  consequent  on  sewer 
construction  is  exceedingly  apt  to  contribute  to  the  disease- 
breeding  slovenliness  in  what  is  often  at  its  best  an 
elongated  Gehenna.  Again,  in  a  narrow  alley  the  space 
available  for  piling  the  excavated  dirt  is  so  contracted  that  the 
cost  of  construction  is  frequently  increased  by  a  very  appre- 
ciable amount  on  this  account.  On  a  side  hill,  however,  it 
may  often  be  advisable  or  even  necessary  to  locate  sewers  in 
the  alleys  for  the  drainage  of  houses  on  the  lower  sides  of 
streets  above. 

Sewers  should  be  laid  in  continuous  straight  lines,  as  far 
as  possible. 


THE  DESIGN. 


103 


No  turn  greater  than  a  right  angle  should  be  made  at  any 
one  point  by  any  sewer  less  than  24  inches  in  diameter,  and 
any  turn  whatever  made  by  such  a  sewer  should  be  in  a  man- 
hole, by  means  of  a  curved  channel.  For  sewers  larger  than 
12  or  15  inches  it  is  advisable  to  use  two  manholes  in  making 


15 


30' 


FIG.  4. — ALIGNMENT  OF  SEWER-JUNCTIONS. 

a  bend  greater  than  45°  (see  Fig.  4).  Brick  or  concrete 
sewers  more  than  24  inches  in  diameter  may  be  laid  on 
curves,  since  they  can  be  entered  for  inspection  or  cleaning. 

Each  lateral  sewer  should  take  the  most  direct  course  to 
its  main,  each  main  the  most  direct  course  to  its  outlet,  and 
the  number  of  mains  should  be  as  few  as  possible.  This 
serves  both  economy  and  sanitary  efficiency. 

The  dead  ends  should  be  made  as  few  as  possible,  even  at 
some  expense  of  additional  excavation,  but  not  by  reducing 
mean  velocities  below  2.5  feet  per  second;  nor  is  it  ordinarily 
serviceable  to  unite  the  upper  ends  of  sewers  flowing  in  oppo- 
site directions. 

House-sewers  should  be  carried  within  reach,  as  regards 
both  horizontal  distance  and  grade,  of  every  lot  in  the 
sewered  district. 

Storm-sewers    should    have  as    few    branches  as  can    be 


104  SEWERAGE. 

made  to  reach  all  the  street-inlets,  to  better  insure  which  such 
inlets  should  be  located  previous  to  the  location  of  the  sewer- 
lines. 

It  is  generally  advisable  to  avoid  crossing  private  property 
where  possible,  since  legal  complications  and  delays  might 
result  from  such  crossing.  This  will  frequently  be  impossible, 
however,  particularly  near  outlets. 

The  sewer-lines  can  usually  be  laid  out  directly  upon  a 
contoured  working  map,  an  approximate  rough  estimate  of 
the  necessary  size  and  consequent  minimum  slope  of  each 
sewer  being  made,  that  deep  or  shallow  cutting  may  be 
avoided.  The  direction  of  flow  should  be  indicated  by 
arrows. 

In  the  separate  system  the  storm-water  sewers  should 
usually  be  placed  on  one  side  of  the  street  centres,  the  house- 
sewers  being  placed  in  the  centres.  The  two  should  never  be 
placed  one  above  the  other  in  the  same  trench  unless  in  con- 
tact with  each  other  or  connected  by  masonry. 

ART.  30.     VODUME  OF  HOUSE-SEWAGE. 

Since  the  grade  of  a  sewer  is  limited  by  its  size,  and  the 
size  is  determined  by  the  grade  and  consequent  velocity,  but 
to  even  a  greater  extent  by  the  maximum  volume  of  sewage 
to  be  carried,  this  last  must  be  determined  before  either  the 
limiting  grade  or  size  can  be  decided  upon.  If  the  maximum 
rate  of  water-consumption  be  taken  at  175  gallons  per  day 
per  capita  the  maximum  volume  per  second  to  be  carried  by 

a  sewer  (in  cubic  feet)  is g  V  86 '  *n  w^^c^  ^  ~  density 

of  population  and  A  =  the  area  in  acres. 

Beginning  at  the  summit  of  each  lateral,  it  is  clear  that  it 
is  unnecessary  to  calculate  the  capacity  required  for  any  sec- 
tion of  sewer  until  the  point  is  reached  where  the  volume  of 


THE  DESIGN.  105 

sewage  to  be  carried  exceeds  the  capacity  of  the  smallest 
sewer  used  at  the  given  grade.  For  an  8-inch  pipe  flowing 
half  full  with  an  average  velocity  of  2.5  feet  per  second  this 

/3.i4i6  X  16  X  2.5       \ 
volume  is    about    ^ -  =  ,(0.4363  cubic  feet 

per  second,  which  would  be  contributed  as  a  maximum  flow 

/0.4363  X  7-48  X  86400       \ 
by   a   population    of    (-  —       =  Jioil,    or 

about  40  acres  having  a  density  of  population  of  40. 

At  the  point  where  the  sewage  from  the  tributary  popula- 
tion  exceeds  the  capacity  of  the  sewer  its  size  must  be 
enlarged  to  the  next  market  size  of  pipe  or  the  next  size  of 
masonry  sewer  convenient  for  construction. 

The  allowance  for  leakage  into  the  sewer  of  ground-water, 
which  should  be  a  small  proportion  of  the  sewage  proper,  may 
be  added  at  intervals,  according  to  the  engineer's  judgment, 
based  on  such  data  as  he  is  able  to  obtain. 

In  calculating  these  volumes  it  is  advisable  to  begin  with 
the  furthermost  lateral  sewer  first;  where  this  joins  another 
the  contributions  of  both  are  to  be  added  to  determine  the 
flow  below  that  point,  and  in  tracing  down  this  line  as  each 
branch  is  encountered  its  contribution  must  be  calculated  and 
added.  Decision  having  been  made,  after  a  study  of  the 
topographical  map,  as  to  the  line  of  sewer  into  which  each 
section  of  undeveloped  territory  will  drain  when  sewered,  the 
sewage  which  this  area  will  ultimately  contribute  should  be 
placed  at  the  heads  of  the  volumes  of  flow  in  this  line. 

An  excellent  method  of  making  these  calculations  is 
shown  on  page  122.  The  sewerage-map  Plate  No.  Ill  was 
used  for  this  table. 

In  this  case  it  is  seen  that  the  capacity  of  an  8-inch  pipe 
at  the  minimum  grade  was  reached  at  the  junction  of  the 
Newcastle  and  Budd  Street  sewers,  but  the  line  down  Budd 
has  I  :  50  as  its  grade,  and  no  increase  of  size  is  yet  necessary. 


io6 


SEWERAGE. 


CALCULATION    OF    SEWAGE    QUANTITIES    AND    SEWER    SIZES. 


Street. 

From 

To 

2  w 
<\ 

Density. 

rt    , 
11 

<r 

£s£ 

S  =  Q 

*3)L 

3J 

ti 

(/) 

u 
1 

o 

1 

!/5 

Prospect 

Walnut 
Walnut 
Liberty  (extended) 
Walnut 

Newcastle 

Prindle 
Prospect 
Newcastle 
Liberty 

Walnut 

Prospect 
Liberty 
Walnut 
Budd 

10.4 

!•? 
1.9 
I*.7 

8.2 

20 

2O 
20 
2O 
2O 

208 
3 

254 
164 

36400 

5Q50 
6750 
44450 
28700 

52So 

9555° 
26250 
i  54000 

38500 



Ji     30 
1  i     ii 

I        20 
I       2O 

I       300 

x    300 

8  in. 
it 

122250 

Newcastle 
Undeveloped   terri 
Newcastle 
Undeveloped   terri 

Prospect 
tory  tributa 
Liberty 
tory  tributa 

Liberty 
ry  to  -Newcastle 
Budd 
ry  to  Budd 

Walnut 
River 
River 

1-5 
27-3 
7-5 
44-o 

I  I  .0 

Jm° 

Gro 

2O 
20 
2O 
20 

20 
2O 

und- 

£ 

150 

880 

220 

60 

water 

281050 
31955° 

I      300 

Sin. 

I   50 

Sin. 

10  " 

Budd 
Budd 
Budd 

Newcastle 
Walnut 
Walnut 

10500 

452300 

At  the  junction  of  Budd  aid  Walnut  the  sewage  amounts  to 
452,300  gallons,  or  42  cubic  feet  per  minute,  and  the  sev/er 
from  there  to  the  river  must  have  the  minimum  grade  allow- 
able. The  size  must  therefore  be  increased,  and  as  the  next 
market  size,  lo-inch,  has  a  capacity  at  that  grade  when  two 
thirds  full  of  about  590,000  gallons,  it  is  therefore  sufficiently 
large  for  the  rest  of  the  line,  including  sewage  contributed 
along  its  length  and  ground-water.  No  ground-water  was 
anticipated  on  the  hill  side,  but  it  was  considered  probable 
that  on  Budd  below  Walnut  this  would  leak  into  the  sewer  at 
the  rate  of  two  gallons  per  day  per  foot  of  sewer  (see  Art. 
46). 

ART.  31.     VOLUME  OF  STORM-SEWAGE. 

The  principles  stated  in  Articles  16-20  will  be  used  as  a 
basis  in  determining  the  amount  of  storm-water  to  be  pro- 
vided for.  Decision  should  first  be  made  as  to  whether  this 
shall  include  run-off  from  storms  of  the  first,  second,  or  third 
class.  Then  the  past  rates  of  fall  of  such  storms  should  be 
ascertained.  If  the  records  of  such  rates  extending  over  a 
series  of  years  are  not  obtainable  use  may  be  made  of  the 
rainfall  data  given  in  Art.  17.  Plate  No.  IV  shows  rainfall- 
curves  for  average  maximum  rains  of  the  second  class,  from 


THE  DESIGN. 


107 


Plate  III, 


io8  SEWERAGE. 

•  \ 

which  may  be  taken  the  amount  of  rain  to  be  expected  during 
any  given  period  of  time  in  the  localities  named.  If  sufficient 
rainfall  data  for  the  place  in  question  are  available  a  similar 
curve  for  that  place  plotted  from  these  data  will  be  found 
serviceable.  If  these  data  have  not  been  kept  by  the  city  it 
is  probable  that  the  rates  for  a  neighboring  city  can  be 
obtained  from  the  Weather  Bureau  at  Washington,  which  now 
has  self -registering  gauges  in  a  great  many  cities  of  the 
United  States. 

Next  to  be  determined  is  the  character  of  surface  of  the 
streets  and  included  areas  in  each  section  drained;  that  is,  the 
amount  of  impervious  surface.  The  safest  course  would  be 
to  assume  that  every  street-surface  is,  or  will  be  made,  wholly 
impervious;  that  the  space  covered  by  each  building  will  also 
be  impervious;  and  that  in  residence  districts  the  remaining 
areas  will  be  30$  to  80$  impervious  at  the  time  of  heavy 
downpours,  since  rainfall  records  show  that  at  least  25$  of 
these  are  preceded  by  one  or  more  hours  of  rainfall,  which 
increase  the  natural  imperviousness.  These  figures  will  be 
used  in  illustrative  calculations  in  this  work;  but  the  judgment 
of  the  engineer,  based  on  local  conditions,  may  well  dictate 
others,  differing  for  each  case  considered.  For  instance,  a 
closely  built-up  business  district  having  paved  yards  and 
courts  may  be  assumed  as  all  wholly  impervious. 

These  points  having  been  decided,  the  inlets  should  be 
located  on  a  contour-map.  Also  it  will  be  well  to  state  in 
figures  on  each  city  block  its  area  and  percentage  of  imper- 
viousness (see  Plate  V). 

The  percentage  of  imperviousness  may  be  calculated  thus: 

Let  /  =  the  average  length  of  a  city  block- 

b=    "        "          breadth  "     " 

f 

/=   *  number  of  front  feet  to  a  building 

lot; 
d=    "        "          depth  of  a  building-lot; 


THE  DESIGN. 


109 


Plate  IV. 
10 


DURATION  OF  RAIN   IN   MINUTES. 
20  30  40  50 


1300 


1200 


RATES  OF  RAINFALL 
STORMS  OF  THE 
SECOND  CLASS. 


CURVE  FOR  OBTAINING 
AREA   IN  ACRES. 


100 


700 


GOO 


500  400  300  200 

WIDTH  OF  AREA  IN  FEET. 


100 


HO  SEWERAGE. 

a  =  the  average  area  covered  by  a  building: 
w  =    "        lt          width  of  street; 

/  =    "  percentage  of  imperviousness  of  yards, 

courts,  etc.,  expressed  as  a  decimal; 

/=    "     percentage   of   imperviousness   of   the   entire 

area,  expressed  as  a  decimal. 
Then 


lb(a  +  ifd  -  id]  +  wfd(l+b  +  w) 


As  an  example,  let  /  —  450,  £  =  250,  f  =  $o,  d-=-  125, 
^  =  1200  sq.  ft.,  w  —  66,  i  =  .60;  then  7—  .777,  or  say  .78. 

When  most  of  the  above  factors  must  be  estimated  by 
judgment  only,  as  for  areas  not  yet  opened  up  or  fully  devel- 
oped, it  may  be  as  well  to  estimate  /  at  once. 

By  comparing  this  formula  with  that  on  page  36  we  see 
that 

lb(a+ifd-  id] 


which  formula  can  be  used  when  P  has  already  been  calcu- 
lated. The  relation  between  I  and  P  will,  it  is  evident,  vary 
in  different  cities  and  also  in  different  parts  of  the  same  city. 
The  map  having  been  thus  prepared,  with  the  a  and  /on 
each  block,  the  uppermost  corner  of  the  drainage-area  furthest 
from  the  outlet  may  be  taken  as  a  starting-point.  If  there 
are  beyond  this  any  areas  not  included  in  the  sewered  districts, 
but  the  run-off  from  which  flows  into  such  districts,  this  run- 
off must  be  estimated  and  provided  for.  For  this  purpose  the 
formula  Q  =  AIR  may  be  used,  A  being  the  total  area,  /the 
coefficient  of  imperviousness,  and  R  the  maximum  rate  of 
rainfall  (of  the  class  to  be  provided  for)  for  that  length  of 


THE  DESIGN.  in 

time  which  will  elapse  while  the  run-off  from  the  furthest 
point  of  the  drainage-area  is  reaching  the  sewer.  This  time 
is  an  uncertain  quantity  and  will  to  a  certain  extent  vary 
with  R.  Some  engineers  assume  a  velocity  of  about  2  feet 
per  second  over  the  surface.  The  formula  v  =  2000!  V S  is 
offered  as  an  empirical  one  for  calculating  the  velocity  of 
run-off  over  the  surface  in  feet  per  minute,  5  being  the  sine 
of  the  slope.  While  /  does  not  directly  affect  this  velocity, 
it  is  observed  that  the  most  impervious  surfaces  usually  offer 
the  least  obstruction  to  the  flow  of  water,  and  vice  versa. 
The  time  /  for  which  r  is  assumed  is  obtained  by  dividing 
v  into  /,  the  length  of  the  furthest  corner  of  the  drainage-area 
from  the  sewer. 

The  same  method  is  also  applied  to  determining  the  time 
of  run-off  from  each  smaller  area  to  its  inlet,  /  in  such  cases 
being  taken  as  the  distance  by  gutter  of  the  furthest  point 
from  its  inlet. 

The  amount  to  run-off  to  each  point  of  interception  thus 
found  must  be  provided  for  by  inlets  of  sufficient  size  and 
number  (see  Art.  36)  and  by  ample  sewer  capacity.  The  fol- 
lowing tabulation  of  a  calculation  by  the  above  method  for 
the  district  shown  in  Plat  V  is  given  as  an  illustration. 


a     is  the  size  of  each  sub-area; 
/     is  its  imperviousness ; 

AI     is  in  each  case  the  sum  of  all  the  preceding  a/'s; 
s     is  the  surface-slope  of  the  sub-area; 

/     is  the  greatest  distance  traversed  by  the  run-off  in  crossing  each  sub-area; 
t     is  the  time  occupied  by  the  run-off  in  travelling  the  distance  I; 
r     is  the  rate  of  rainfall  for  the  time  t; 
q  =  alr. 

S     is  the  slope  of  the  sewer  removing  the  run-off  from  the  point  in  question; 
L     its  length  to  the  point  next  considered  (usually  the  next  inlet  or  sewer- junction) ; 
T     is  the  time  occupied  by  the  run-off  in  flowing  from  the  extreme  limit  of  the 

drainage-area  A,  over  the  surface  and  through  the  sewers  to  the  point 

under  consideration; 

R     is  the  rate  of  rainfall  for  the  time  T; 
Q      is  the  total  amount  of  run-off  from  all  drainage-areas  above  =  AIR. 


112 


SEWERAGE. 


Plate  V. 


STREET 


2ND 


STREET 


1  —              —  n 
i 

1 

1 

ij 

#4 

#5 

°°i 

*6 

i 

ct—  3  6       ^ 

a—  3.6 

a=3.6 

^r 

DO 

QJ 

u 

I=.8U 

I=.80 

i 

7=.80 

,  i 

r* 

c; 

'  i 

n                               n 

/- 

~^-s-^o8~— 

>* 

?  487>"S~.004 

^- 

~  STREET 

UJ 

UJ 

jv 

UJ 

Tr  7 

ID 

'  8 

13 

//  y 

D 

a=3.6      | 

Z 
UJ 

a=3.6 

Z 
UJ 

a=3.6 

Z 
Ul 

I=.80 

5 

J=.80 

7=.80 

4TH 

>     DIRECTIONlOF  FLOW  I 

3  INLET 

»  MANHOLE  I 


STREET 


THE  DESIGN. 


vQ           O*         OO        Ot 

'ox     o 

3         3 
o>        rt 

.  3*      s* 

:r^ 

09 

- 

O 

Undeveloped  territory 

Location  of  Area. 

M              M            CO            CO 

CO          CO 

en 

to 
en 

to 

en 

t 

• 

CO          CO          CO          CO 

O         O         0         O 

CO          OO 

o      o 

co 

o 

CO 

O 

co 
O 

g 

H 

M              M             tO             tO 

4i        •£•         oo        oo 
4*        4i,         oo        GO 

to        to 

oo        oo 
oo        co 

to 

b 

to 

b 

to 

b 

to 

4- 

s, 

4^.          10          M          co 

4^        vO        en         ON 
O          ON         tO         4^ 

CO          CO 

•>J           CO 

ON         CO 

* 

to 

oo 

to 

ON 

to 

s 

8888 

vj        en        ^J        en 

8     2 

^J          CO 

b 

M 

b 

M 

b 

M 

b 

en 

- 

ON         ON         CO         CO 

^^88 

CO          CO 
CO          CO 

0         0 

ON 

en 

ON 
en 

ON 

to 
en 

CO 

1 

N 

4>        tn         O\       ^J 

O\        .C- 

Oo 

Oo 

Oo 

M 

•h 

^»          ON        O          M 

to           ON 

vO 

00 

vO 

4i. 

Oo         OJ         OJ         Oo 

Oo         OJ 

OJ 

Oo 

OJ 

to 

^ 

•N*      in      4k       ta 

Oo         -^1 

CO 

CO 

CO 

Cn 

* 

en        en        0        0 

vO         0 

^, 

^, 

^, 

8s 

OJ          O          CO         to 

en         ON 

ON 

ON 

ON 

0 

"* 

8 

4k 

8 

8 

| 

1 

c, 

ON 

ON 
to 

? 

OJ 

OJ 

j 

to 

OJ 
4*. 

to 

to 

to 
en 

* 

? 

ON 

to 
b 

ON 
to 

4k 

p 

b 

0 

Cn 

to 

to 

^ 

1^ 

i^ 

Size  of  Sewer. 

4k 

8 

OJ 

§r 

OJ 

to 
to 

8 

Velocity  of  Flow. 
Feet  per  Minute. 

oo 

CO 

o 

en 

o 

CO 

0 

CO 

h 

3d  St.  ,  Ave.  C  to  Ave.  D. 

3d  St.,  Ave.  B  to  Ave.C. 

<5 

? 

n 

to 
At 

CO 

o 

CO 

CO 

to 

0. 
CO 

n 

CO 
o 

n 
p 

n 

a 

C/l 

O 
to 

CL 

CO 

Location  of  Sewer 

H4  SEWERAGE. 

The  quantity  q(=alr)  as  well  as  Q  should  be  calculated  for 
each  sub-area,  and  if  the  Q  for  any  stretch  of  sewer  is  at  any  place 
less  than  the  q  immediately  tributary  to  the  same  the  latter  should 
determine  the  size. 

Plate  IV  will  be  found  convenient  for  determining  a,  and 
also  R  when  the  rates  of  rainfall  of  the  place  in  question  can 
be  represented  by  any  of  the  curves  there  given,  these  being 
for  rains  of  the  second  class.  To  find  a  in  acres  from  the 
diagram,  use  one  dimension  (in  feet)  of  the  area  (or  of  an 
equivalent  rectangle  if  it  is  not  rectangular)  as  an  ordinate 
and  find  the  corresponding  abscissa  of  the  acre-curve  in  the 
diagram;  divide  this  into  the  other  dimensions  of  the  area  and 
the  quotient  will  be  a  in  acres. 

By  the  table  the  run-off  from  the  undeveloped  territory  is 
placed  at  60.0  cubic  feet  per  second,  which  is  carried  by  a 
42-inch  sewer  on  a  .6%  grade  for  360  feet,  where  it  receives 
still  more  sewage;  the  maximum  amount  to  be  received  there, 
both  over  the  surface  and  through  the  sewer,  being  62.4  cubic 
feet,  although  q  for  the  block  No.  i  alone  is  7.6  cubic  feet. 
But  Q  is  not  equal  to  60.0  +  7.6,  because  the  latter  quantity 
was  due  to  a  rainfall  of  3.9  minutes'  duration,  or  rather  to 
the  maximum  rate  for  that  time,  during  which  only  such 
water  would  have  arrived  from  the  upper  end  of  the  drainage- 
area  as  was  due  to  a  lower  rate  of  rainfall;  but  the  time  of 
14.3  minutes  is  that  for  which  the  run-off  is  calculated  from 
both  the  undeveloped  territory  and  block  No.  i.  Blocks 
No.  2  and  No.  3  both  reach  the  sewer  at  the  same  point,  and, 
taking  the  rate  of  rainfall  for  15.1  minutes,  we  have  a  total 
run-off  from  all  the  territory  above  of  72.0  cubic  feet  pet 
second  and,  the  grade  being  .5%,  a  44-inch  sewer  is  found  to 
be  necessary. 

Blocks  No.  4  and  No.  7  discharge  first  into  a  branch 
sewer,  which  it  is  found  should  be  24  inches  in  diameter. 
Where  this  joins  the  main  the  run-off  from  blocks  No.  5  and 


THE   DESIGN.  II 5 

No.  8  and  from  half  of  No.  6  and  No.  9  also  reaches  it,  and  it 
must  consequently  be  increased  in  size.  The  time  T  at  this 
point  is  13.4+0.9  (in  the  Ave.  B  sewer) +0.8  (in  the  Second 
Street  sewer) +1.3  (in  the  Ave.  C  sewer),  or  16.4  minutes, 
and  the  rate  of  rainfall  for  thie  time  is  used  for  the  run-off 
from  the  entire  area. 

It  will  be  seen  that  the  method  here  employed  is  but  a 
practical  application  of  the  principles  stated  in  Art.  13. 
More,  and  more  accurate,  data  for  determining  t  and  /,  as 
well  as  R,  are  needed  before  this  or  any  method  can  be  relied 
upon  to  give  more  than  general  approximations  to  the  run-off. 
Fortunately  with  the  method  here  given  the  approximation 
becomes  more  close  as  the  area  becomes  more  urban,  and  is 
most  so  in  the  most  densely  populated  districts,  where  the 
danger  from  gorged  sewers  would  be  greatest. 


ART.  32.     GRADE,  SIZE,  AND  DEPTH  OF  SEWERS. 

For  both  determining  and  recording  the  grades  of  the 
proposed  sewers  use  is  usually  made  of  the  profiles  of  the 
streets,  plotted  from  the  level  notes.  Upon  these  a  vertical 
longitudinal  section  of  the  proposed  sewer  through  its  centre 
line  is  placed,  thus  showing  the  size,  grade,  and  depth  of  the 
sewer.  While  designing,  however,  it  will  be  found  convenient 
to  pencil  in  the  line  of  the  invert  only,  since  then  changes  in 
its  vertical  location  can  more  readily  be  made. 

A  short  experience  in  sewer-designing  will  demonstrate 
how  mutually  involved  are  Q,  5,  the  diameter  and  the  depth 
of  the  sewer.  In  many  cases  it  will  be  necessary  to  alter  and 
realter  the  grade  and  diameter  before  obtaining  for  each  reach 
of  sewer  the  best  obtainable  depth  and  velocity.  Q  is  a  fixed 
quantity  for  any  given  case,  5  may  vary  between  fixed  limits, 
the  size  also  has  its  limits  in  some  cases,  but  the  depth  of  the 


II 6  SEWERAGE. 

sewer  may  vary  from  any  distance  below  to  any  distance  above 
ground.  A  depth  of  25  or  30  feet  is  obtained  in  many 
sewerage  systems,  and  even  50  feet  or  more  has  been  reached 
in  open  cut,  while  sewers  have  been  laid  in  tunnel  at  still 
greater  depths.  Where  possible  deep  sewers  should  run 
through  wide  streets,  that  the  danger  to  building-foundations 
may  be  kept  as  small  as  possible;  and  they  should  avoid  the 
busiest  thoroughfares  unless  these  are  also  the  widest  streets 
and  the  soil  is  treacherous.  The  sewer  may  in  some  cases  be 
carried  on  bridges  or  trestles,  as  in  crossing  a  stream  or  ground 
lower  than  the  hydraulic  gradient.  In  many  such  locations, 
however,  this  position  will  be  impossible,  owing  to  traffic  on 
the  river,  to  danger  from  floods,  to  blocking  of  streets,  or  to 
prohibitive  cost  of  construction.  In  such  cases  the  pipe  may 
be  placed  under  the  surface  of  the  ground  or  in  the  bed  of 
the  stream,  being  thus  below  the  hydraulic  gradient.  Such  a 
downward  loop  is  called  an  inverted  siphon.  Many  instances 
of  these  are  in  use,  and  if  care  be  taken  in  their  design  and 
construction  they  need  give  no  trouble.  It  will  not  be  possi- 
ble, or  at  least  advisable,  to  connect  any  buildings  to  an 
inverted  siphon,  since  the  sewage  will  continually  stand  in 
the  connections  up  to  the  level  of  the  hydraulic  gradient  of 
the  siphon. 

The  depth  of  storm-sewers  is  usually  fixed  by  grade 
requirements  only;  the  covering  over  them,  however,  should 
be  not  less  than  two  feet  and  would  better  be  three  or  four 
feet.  The  minimum  depth  to  which  house  or  combined 
sewers  should  be  laid  will  usually  be  decided  by  local  circum- 
stances or  customs.  It  is  generally  desirable  to  lay  them 
somewhat  deeper  than  the  gas-  or  water-pipes,  that  these  may 
not  interfere  with  them.  The  city  of  Brooklyn  some  years 
ago  fixed  12  feet  as  the  depth  to  which  all  (combined)  sewers 
are  to  be  laid,  unless  the  maintenance  of  proper  velocity 
requires  a  less  or  greater  one.  In  Philadelphia  14  feet  is  the 


THE  DESIGN.  117 

standard  depth,  in  Washington,  D.  C.,  10  feet.  In  residence 
districts  in  the  smaller  cities  7  to  10  feet  is  usually  sufficient, 
although  in  a  street  running  along  a  hillside  a  much  greater 
depth  may  be  called  for  by  the  depth  of  basements  upon  the 
lower  side  of  the  street.  In  streets  which  are  already  built 
up  the  sewer  should  be  deep  enough  to  drain  all  basements 
and  cellars,  with  the  exception,  perhaps,  of  an  occasional  one 
of  unusual  depth.  To  insure  this  the  cellar  depths  taken 
during  the  survey  should  be  indicated  in  their  proper  positions 
upon  the  profiles  of  their  respective  streets.  In  many 
Southern  cities  where  there  are  no  cellars  under  the  dwellings 
and  there  is  little  danger  of  frost  the  sewers  may  be  given  a 
depth  of  covering  of  only  3  or  4  feet.  In  the  North  6  feet  is 
probably  the  least  depth  which  should  be  given  to  the  flow- 
line  save  under  exceptional  circumstances.  The  maximum 
depth  should  be  kept  at  14  to  16  feet  if  possible,  since  below 
this  the  cost  rapidly  increases.  When  the  depth  is  consider- 
able the  expense  of  making  house-connections  may  become 
excessive.  It  may  in  such  cases  be  found  cheaper  to  lay  a 
small  sewer  about  7  or  8  feet  below  the  surface  and  following 
the  surface  grade,  which  may  be  with  or  against  the  grade  of 
the  deep  sewer,  to  a  manhole  in  the  deep  sewer  into  which 
this  shallow  one  can  discharge. 

Before  fixing  the  grade  it  is  well  to  prepare  tables  similar 
to  those  given  in  Articles  35  and  36,  and  also  to  calculate  as 
closely  as  possible  the  total  amount  of  sewage  reaching  each 
outlet. 

Very  often  the  main  sewer  for  a  long  distance  from  the 
outlet  must  be  laid  at  a  minimum  grade  if  pumping  is  to  be 
avoided  or  the  lift  kept  as  small  as  possible.  In  such  a  case 
the  grade  of  this  main  will  be  the  first  to  be  located  upon  the 
profile,  the  outlet  being  placed  as  low  as  is  permissible.  This 
should  never  be  below  ordinary  high  water  unless  absolutely 
necessary,  and  under  no  consideration  should  it  be  below  or 


Il8  SEWERAGE. 

even  as  low  as  ordinary  low  water;  or  rather  this  should  be 
true  for  the  hydraulic  gradient,  although  the  last  few  feet  of 
the  sewer  may  be  given  a  steeper  grade  to  bring  the  outlet 
below  the  water-surface  or  into  the  channel. 

There  may  be  other  lines  also  where  the  surface  elevations 
demand  the  flattest  possible  grades;  that  is,  the  grades  which 
will  give  the  minimum  permissible  velocity.  This  grade  will 
depend  upon  the  size  of  the  sewer,  and  this  again  upon 
the  quantity  of  sewage.  To  ascertain  this  size,  reduce  the 
maximum  sewage  flow  to  cubic  feet  per  second,  divide  by  the 
desired  velocity  of  flow  in  feet  per  second,  multiply  the 
quotient  by  1.5  for  mains  or  2  for  laterals,  and  find  the  diam- 
eter of  a  circle  having  this  product  as  its  area,  which  will  be 
the  sewer  diameter  required.  Or,  divide  the  gallons  of 
sewage  per  day  times  1.5  or  2,  as  the  case  may  be,  by  the 
•required  velocity  in  feet  per  second,  and  take  the  size  corre- 
sponding to  the  next  highest  quantity  in  the  following  table: 

TABLE  No.  16. 

Sizeofsewer 8"            10"            12"            15" 

Gallons  of  sewage  per  day 225,500     352,500     507,600     792,800 

v 

Size  of  sewer 18"                20"                 24" 

Gallons  of  sewage  per  day 1,141,700      1,410,300       2,030,500 

v 

Where  possible  the  grades  of  house-sewers  should  be  such 
as  to  give  a  velocity  of  from  3  to  4  feet  per  second,  and  those 
of  storm-sewers  from  4  to  5  feet  per  second.  The  demands 
of  economical  construction  and  the  necessity  for  sufficient  fall 
in  house-connections  should  not,  however,  be  sacrificed  to 
reduce  velocities  to  less  than  10  or  12  feet,  which,  however, 
should  be  the  maximum  allowed. 

If  it  is  possible  the  grade  of  the  various  sewers  should  be 
so  proportioned  that  the  velocity  of  the  sewage  shall  increase 
as  the  outlet  is  approached,  or  at  least  it  should  not  decrease, 


THE  DESIGN.  119 

since  a  decrease  in  velocity  may  cause  a  deposit  of  suspended 
matter.  Frequently,  however,  it  is  impossible  to  attain  this 
in  the  design,  since  the  flattest  surface  slopes  are  usually 
nearest  to  the  outlet  and  the  sewer  grades  are  largely  con- 
trolled by  these. 

From  the  formulas  Q  =  aV  and  V  =•  cVRS,  considering 
the  sewer  as  flowing  full,  and  giving  c  a  constant  value  of  85, 
which  will  in  no  case  vary  more  than  10$  from  Kutter's  c  for 
pipes  ranging  from  8  to  18  inches  diameter,  we  have  the 
formula 


=  .0796C'S'Q, 
or 


V  being  in  feet  and  Q  in  cubic  feet  per  second.  This  formula 
should  not  be  used  where  any  considerable  accuracy  is 
demanded,  but  will  be  found  convenient  for  use  in  fixing  the 
first  approximate  grades.  If  V  is  to  be  a  constant  5  must  vary 
inversely  as  V  Q. 

Sj  however,  equals  -j  if  /  equals  the  fall  of  the  grade  for 

a  length  /.  If  /,  /',  /",  etc.,  be  taken  as  the  lengths  between 
successive  manholes,  /,  /',  /",  etc.,  as  the  corresponding 
falls,  and  Q,  Q  ',  Q",  etc.,  as  the  quantities  of  sewage  flowing 
through  these  lengths,  then  (if  V  is  constant) 


also/  +  /'  +  /"  +  etc.  =  F,  the  total  fall  from  the  head  to 
the  outlet  of  the  system.  Knowing  F,  and  /  and  Q  for  each 
length  between  manholes,  we  can  obtain  the  values  of/,/', 
/",  etc.  As  just  stated,  it  is  seldom  that  an  entire  system 
can  be  designed  to  give  a  constant  velocity  to  the  sewage, 


120  SEWERAGE. 

but  this  is  sometimes  possible  in  separate  drainage-areas,  a 
constant  velocity  being  obtained  in  each  area. 

Still  more-  important  than  obtaining  a  constant  or  con- 
stantly increasing  velocity  is  the  keeping  of  the  velocity  within 
the  limits  given  in  Art.  17.  If  the  ground -surf  ace  is  too  flat 
to  permit  of  obtaining  this  velocity  by  gravity,  pumping  must 
be  resorted  to  (see  Art.  37).  If  the  surface  is  steeper  than  is 
permissible  for  the  sewer  the  sewer  grades  can  be  broken  and 
a  drop  made  at  each  manhole  (see  Art.  36). 

A  slight  drop  in  the  grade  should  be  made  at  each  manhole 
on  flat  grades  to  compensate  for  the  obstruction  offered  by  curves, 
etc.,  at  this  point,  and  for  slight  errors  in  measurement;  0.02  or 
0.03  foot  is  usually  sufficient.  This  is  generally  unnecessary  in 
the  case  of  masonry  sewers  or  others  with  continuous  inverts 
with  straight  alignment. 

Of  the  above  principles  the  most  important  is  that  the 
velocity  of  the  sewage  shall  be  within  the  proper  limits;  then 
that  all  basements  and  cellars  to  a  reasonable  depth  shall  be 
drained  by  house-sewers;  also  the  depth  of  excavation  should 
be  kept  as  light  as  possible,  and  the  principles  outlined  in 
Art.  29  should  be  regarded.  The  obtaining  of  the  nearest 
possible  approach  to  an  ideal  design  will  usually  require  many 
changes  in,  and  rearrangement  of,  both  lines  and  grades,  since 
a  change  in  those  of  one  lateral  may  in  some  way  affect  the 
entire  system. 

The  preliminary  grades  having  been  thus  fixed  according 
to  the  desirable  depths  and  velocities  of  flow,  the  size  of  the 
sewer  for  each  reach  should  be  calculated  or  taken  from  the 
diagram  and  the  velocities  checked  by  accurate  calculation. 
Additional  changes,  usually  slight,  will  probably  be  required 
to  obtain  the  best  values  for  each  interdependent  velocity, 
size,  and  depth.  The  junctions  and  crossings  of  the  sewer-lines 
must  be  carefully  examined  and  adapted  to  each  other.  It  is 
a  good  plan  to  make  a  list  of  all  the  manholes,  showing;  for 


THE   DESIGN.  121 

each  the  elevation  at  which  each  sewer  enters  and  leaves 
it.  Two  sewer-lines  should  never  intersect  each  other,  each 
having  a  continuous  grade;  either  one  should  discharge  from 
both  directions  into  the  other  or  they  should  cross,  the  one 
above  the  other. 

At  junctions  the  surface  of  the  sewage  in  the  contributing 
sewer  should  never  be  designed  to  be  lower  than  that  in  the 
other;  that  is,  if  they  are  both  branch  sewers  the  centre  of 
the  tributary  should  not  be  below  the  centre  of  the  intercept- 
ing sewer;  if  the  larger  is  a  main  the  centre  of  the  smaller 
should  not  be  lower  than  a  point  two  thirds  the  diameter  of 
the  larger  above  its  invert.  It  would  be  still  better  to  place 
the  invert  of  the  tributary  above  the  sewage-surface  in  the 
interceptor,  particularly  when  the  former  drains  but  a  small 
district;  but  where  the  total  fall  possible  is  slight  none  of  it 
need  be  utilized  for  this  purpose. 

Difficulty  will  sometimes  be  found  in  so  arranging  the 
comparative  depths  of  storm-  and  house-sewers  that  the 
house-connections  can  pass  under  or  over  the  former.  In 
some  cases  this  may  be  impossible,  and  it  may  be  necessary 
to  place  a  house-sewer  on  each  side  of  the  storm-sewer. 

Reference  to  the  data  of  locations  and  depths  of  gas-  and 
water-pipes  and  other  existing  sub-surface  systems  should  be 
constantly  made  and  the  sewers  so  designed  as  to  interfere 
with  them  as  little  as  possible. 

On  the  profile  of  each  sewer-line  the  elevation  of  all  trans- 
verse sewers  should  be  indicated  and  a  cross-section  of  the 
sewer  shown.  On  the  finished  profile  it  is  well  to  indicate 
the  thickness  and  material  of  the  sewer-walls  and  of  all  man- 
holes, lamp-holes,  and  other  appurtenances.  The  materials 
may  be  indicated  by  colors,  as  red  for  brick,  brown  for  sewer- 
pipe,  etc.  The  grade,  length,  and  size  of  the  sewer  between 
each  two  manholes  should  be  given  in  figures,  as  well  as  the 
exact  elevation  of  the  invert  at  each  change  of  grade. 


122  SEWERAGE. 


ART.  33.     INVERTED  SIPHONS. 

Since  the  ordinary  sewer  is  designed  to  flow  only  \  to  § 
full,  while  an  inverted  siphon,  being  under  a  head,  will  flow 
full  bore,  the  velocity  in  the  latter  will  be  only  i  to  f  that  in 
the  sewer  laid  to  the  hydraulic  gradient,  if  they  are  of  the 
same  size.  On  account  of  the  difficulty  of  access  and  repairs 
it  is  especially  necessary  that  the  velocity  of  flow  in  the  siphon 
should  be  at  least  as  great  as  that  in  the  ordinary  sewer,  that 
deposits  may  be  prevented.  This  can  be  attained  only  by 
reducing  the  size  of  the  siphon-pipe.  Moreover,  this  velocity 
should  be  had  from  the  beginning  of  the  use  of  the  system; 
and  therefore  this  size  should  be  designed  to  give  sufficient 
velocity  to  the  sewage  from  the  first.  This  first  sewage  flow 
may  be  doubled  or  trebled  as  time  passes,  and  the  increase 
may  then  be  provided  for  either  by  giving  sufficient  fall  to  the 
siphon  originally  to  produce  the  greater  velocity  necessary  or 
by  additional  siphon-pipes.  Usually  at  least  two  siphon- 
pipes  are  laid  at  the  first,  that  while  one  is  being  emptied 
and  cleaned  the  other  may  be  used.  The  friction-head  in  the 
inverted  siphon  will  be  greater  than  if  the  sewer  were  laid  to 
the  hydraulic  gradient,  and  consequently  the  gradient  must 
be  steeper.  The  difference  in  elevation  of  the  two  ends  of 
the  siphon  should  be  equal  to  the  fall  required  by  a  sewer  of 
the  same  size  flowing  full  and  of  the  length  of  the  entire 
siphon  (which  is  not  the  horizontal  distance  between  its  ends) 
to  pass  the  given  amount  of  sewage. 

The  velocity  of  flow  in  an  inverted  siphon  is  entirely  inde- 
pendent of  the  fall  therein,  but  depends  upon  the  quantity 
of  sewage,  since  all  of  this  must,  but  no  more  can,  pass 
through  it.  If  the  fall  in  the  inverted  siphon  is  not  sufficient 
the  sewage  will  back  up  the  sewer  until  sufficient  head  is 
obtained  to  produce  the  required  velocity.  Hence  to  prevent 


THE   DESIGN. 


123 


this  the  fall  in  the  siphon  itself  should  be  made  great  enough 
to  create  the  velocity  which  will  be  required  by  the  largest 
quantity  to  be  passed  at  any  time. 

An  inverted  siphon  may  at  times  be  necessary  for  passing 
under  some  obstruction  in  the  street — as  a  large  conduit  of 
one  kind  or  another,  but  this  should  be  avoided  where 
possible. 

For  details  of  inverted-siphon  construction  see  Articles  44 
and  72. 

ART.  34.     SUB-DRAINS. 

Very  frequently  storm-sewers  are  placed  at  such  a  short 
distance  from  the  surface  that  they  cannot  be  utilized  for 
draining  damp  cellars,  particularly  since  a  cellar  should  be 
connected  with  no  sewer  whose  crown  is  above  its  level,  from 
danger  of  back-water  when  the  storm-sewer  flows  full. 
Ordinarily  the  house-sewer  is  below  the  cellar-level;  but  this 
should  not  be  utilized  as  a  drain,  both  because  the  amount  of 
s'ewage  may  thus  be  too  largely  increased ;  and  still  more  on 
account  of  the  danger  from  sewer-air,  which  would  have  free 
access  through  the  drain  should  the  trap-seal  evaporate  during 
a  drought,  which  it  is  very  apt  to  do,  and  from  the  cellar  this 
air  might  permeate  the  entire  house. 

From  a  sanitary  point  of  view  the  drainage  of  wet  soils 
is  almost,  if  not  quite,  as  important  as  the  sewerage  and 
should  not  be  neglected.  The  mere  opening  of  sewer-trenches 
tends  to  drain  the  soil,  even  after  they  are  refilled.  But  in 
many  cases  it  is  extremely  desirable  to  provide  other  and 
more  positive  drainage. 

It  is  almost  impossible  to  make  a  perfectly  tight  sewer 
without  great  expense,  and  when  laid  in  wet  ground  sewer- 
joints  may  admit  in  the  aggregate  large  quantities  of  water. 
This  could  be  prevented  and  the  land  adjacent  drained,  to  its 


124  SEWERAGE. 

great  improvement  and  the  health  of  residents  thereon,  if  this 
ground-water  could  be  lowered  along  the  trench  by  some 
means. 

During  construction  in  wet  ground  much  trouble  will  be 
experienced,  even  when  the  pumping  facilities  are  ample,  by 
water  rising  and  flowing  over  newly  laid  inverts,  to  their  per- 
manent injury  (see  Arts.  70  and  71). 

These  difficulties  can  each  and  all  be  met  in  most  cases 
by  the  use  of  sub-drains — that  is,  drains  laid  a  little  below  the 
sewers.  These  are  ordinarily  laid  in  a  narrow  trench  in  the 
bottom  of,  and  at  one  side  or  in  the  centre  of,  the  sewer- 
trench.  Their  use  for  construction  drainage  will  be  consid- 
ered in  Part  II.  When  properly  designed  for  this  purpose 
their  size  will  in  most  cases  be  sufficient  for  the  continuous 
drainage  of  the  land  and  also  for  cellar-drainage.  The  in- 
stances will  be  very  few,  however,  in  which  any  approach  to 
an  accurate  estimate  can  be  made  of  the  amount  of  sub- 
drainage  which  will  be  required  in  a  system.  But  provision 
should  always  be  made  for  sub-drainage  wherever  the  soil  is 
wet,  for  permanent  drainage  if  for  no  other  purpose. 

The  water  flowing  into  such  drains  must  have  some  outlet, 
and  the  most  natural  course  would  be,  when  the  sewage  is 
disposed  of  by  dilution,  to  place  the  outlets  of  sewers  and 
sub-drains  at  the  same  point.  It  may  happen,  however,  that 
the  necessity  for  sub-drains  is  not  foreseen  when  the  sewer- 
outlet  is  being  built;  or  the  place  where  they  will  be  neces- 
sary may  be  so  far  from  this  outlet  that  a  great  length  of 
otherwise  useless  drain-pipe  must  be  laid  to  reach  it;  also  the 
amount  of  ground-water  may  be  so  much  greater  than  was 
anticipated,  in  spite  of  all  investigations,  that  the  drain-pipe 
near  the  outlet  will  not  carry  it  all.  In  any  of  these  cases 
another  outlet  may  be  desirable  or  necessary.  This  can  fre- 
quently be  found  by  leading  the  sub-drain  in  a  special  trench 
to  a  near  storm-sewer  or  natural  watercourse.  In  some 


THE  DESIGN.  125 

cases,  however,  special  means  must  be  resorted  to,  such  as 
one  of  the  methods  of  pumping  (see  Art.  37). 

If  the  sub-drain  is  necessary  for  construction  purposes  only 
it  may  be  led  to  a  sump-well  where  a  pump  is  stationed,  and 
broken  and  sealed  at  several  points  after  construction  is  com- 
pleted. (This  last  will  be  necessary,  as  otherwise  the  drain 
would  continue  to  lead  the  ground-water  to  this  point,  which 
might  become  permanently  and  dangerously  water-soaked.) 

Although  the  sub-drain  is  in  most  cases  smaller  than  the 
sewer,  it  must  be  laid  at  practically  the  same  grade.  The 
objection  to  flat  grades  in  house-sewers  does  not  apply  to 
these  so  urgently,  however,  since  the  water  flowing  through 
them,  after  construction  is  completed  at  least,  is  usually  free 
from  suspended  matter  likely  to  cause  deposits.  The  size  and 
position,  then,  are  the  only  elements  of  the  general  design  to 
be  decided  upon.  The  size  it  will  not  be  advisable  to  make 
less  than  6  inches  at  the  outlet  or  for  long  stretches,  but  for 
stretches  of  a  few  hundred  feet  only  and  through  ground  but 
moderately  wet  4-  or  even  2-inch  pipe  may  be  used.  Pipe 
larger  than  10  or  12  inches  is  seldom  used  in  any  but  excep- 
tional cases.  If  a  larger  would  be  required  (and  instances  can 
be  named  where  the  sub-drainage  from  a  small  town  would 
more  than  fill  a  36-inch  pipe)  special  methods  may  be  em- 
ployed; such  as  dividing  the  sub-drainage  system  into  small 
sub-systems,  each  having  its  own  outlet,  which  may,  when 
constructed  under  a  storm-sewer,  discharge  into  the  sewer 
immediately  above  it  or  which  may  be  at  a  near  water- 
course. 


ART.  35.     HOUSE-  AND  INLET-CONNECTIONS. 

The  connections  between  the  sewers  and  opposite  houses 
and  storm-water  inlets  are  of  an  importance  second  only  to  the 
sewer-mains.  Any  defect  in  one  of  the  connections,  while 


126  SEWERAGE. 

limited  in  the  range  of  its  effect,  is  fully  as  detrimental  within 
that  range  to  the  proper  working  of  the  system  as  a  defect 
in  the  main  itself.  Since  the  house-connections  are  subject 
to  extreme  fluctuations  of  discharge  and  hence  to  stoppages, 
as  also  to  the  formation  of  grease  deposits,  it  is  desirable  that 
they  be  equally  as  accessible  as  sewer-mains  for  both  inspec- 
tion and  cleaning,  and  also  that  their  grade  and  alignment  be 
given  equal  care  in  both  the  design  and  the  construction. 
They  should,  if  possible,  be  given  a  uniform  grade  of  not  less 
than  2\%.  Where  the  house  sits  back  from  the  street  an 
observation-hole  (see  Art.  42)  should  be  placed  at  the  fence- 
line,  and  one  should  be  placed  wherever  there  is  a  change  in 
the  line  or  grade.  There  should  also  be  a  hand-hole  in  the 
pipe  just  after  it  enters  the  cellar.  The  junction  with  the 
sewer  should  be  made  by  means  of  branches,  either  Y  or  T. 
It  should  never  be  made  in  pipe  sewers  by  breaking  a  hole 
into  the  shell  and  inserting  a  pipe.  If  the  sewer  be  larger 
than  20-  to  24-inch  a  T  is  advisable,  both  because  this  offers 
easier  inspection  of  the  house-connection  from  its  lower  end, 
which  inspection  can  be  made  by  a  person  entering  the  sewer, 
and  because  the  branch  can  be  placed  entirely  above  the 
ordinary  level  of  the  sewage,  which  position  it  should  occupy 
when  possible  so  as  to  cause  no  interference  with  the  sewage 
flow.  When  the  sewer  is  too  small  to  admit  a  man,  which 
size  will  also  not  admit  of  raising  the  branch  entirely  above 
the  ordinary  sewage  flow  without  giving  it  too  steep  a  pitch, 
a  Y  branch  is  preferable,  because  this  will  retard  the  flow  less 
than  a  T,  and  because  the  house-sewage  will  enter  the  sewer 
at  a  less  angle  with  its  flow.  The  vertical  angle  which  the 
branch  makes  with  the  horizontal  should  not  ordinarily  ex- 
ceed 45°  in  small  sewers,  because  of  the  interference  with  the 
flow  and  of  the  splashing  caused  by  a  vertical  drop  of  sewage 
into  their  relatively  small  stream,  and  because  of  the  danger 


THE  DESIGN.  127 

that  the  weight  of  the  house-connection  may  break  in  the 
crown  of  the  sewer. 

It  is  well  to  so  place  the  branch  in  masonry  sewers  that  a 
trickling  discharge  from  it  will  flow  over  the  surface  for  the  least 
possible  distance,  that  deposits  from  such  discharge  may  be 
avoided.  In  the  case  of  combined  sewers  this  would  call  for 
placing  the  branch  but  a  short  distance  above  the  invert,  but 
it  should  be  given  such  a  grade  as  to  bring  it  higher  than  the 
crown  of  the  sewer  when  it  reaches  the  cellar. 

Some  engineers  always  use  T  branches,  more  always  use 
Y  branches,  for  house-connections;  but  the  practice  here 
recommended  seems  to  best  utilize  the  advantages  and  avoid 
the  disadvantages  of  each. 

The  connections  with  inlets  should  never  enter  the  sewer 
at  an  angle  with  its  axis  greater  than  45°,  on  account  of  the 
great  disturbance  to  the  flow  which  would  be  occasioned. 
Where  possible,  and  particularly  in  small  sewer-mains,  a 
manhole  should  be  placed  where  each  connection  enters  the 
sewer  and  the  connection  continued  by  a  curved  invert  in  the 
bottom  of  said  manhole  (see  Plate  VIII,  Fig.  5). 

It  is  difficult  to  calculate  the  proper  size  for  a  storm-water 
connection,  but,  since  there  is  little  disadvantage  in  having  it 
larger  than  is  actually  required,  while  the  effect  of  too  small 
a  pipe  may  be  disastrous,  it  is  advisable  to  make  the  size  fully 
ample  to  discharge  all  the  run-off  from  the  heaviest  storms. 
A  12-inch  pipe  is  probably  the  smallest  which  should  ever  be 
used;  while  a  24-inch  may  be  required  if  the  sewer  lies  near 
the  surface  (thus  giving  little  fall  to  the  connection)  and  if  the 
tributary  area  is  large.  Where  considerable  undeveloped 
territory  drains  into  the  head  of  a  sewer-main,  or  a  small 
stream  is  there  received,  it  may  be  necessary  to  continue  the 
sewer  to  the  inlet,  not  only  not  diminished  in  size  but  even 
enlarged  into  a  bell  mouth.  It  would  be  advisable  to  use  an 


128  SEWERAGE. 

increase!  at  the  upper  end  of  every  inlet-connection,  since, 
owing  to  the  churning  of  the  water  in  the  inlet,  a  "standard 
orifice"  will  not  pass  more  than  two-thirds  the  water  which 
can  be  carried  by  a  pipe  of  the  same  size. 

ART.  36.    MANHOLES,  INLETS,  FLUSH-TANKS,  ETC. 

The  necessity  for  frequent  connections  between  the  air  of 
the  sewer  and  the  outer  air  has  been  shown  (Articles  23  and 
24).  As  one  means  for  this,  and  one  which  can  always  be 
adopted,  manholes  should  be  adapted  to  serve  this  end  by 
having  perforated  covers.  For  this  purpose,  also,  the  more 
numerous  they  are  the  better.  The  other  and  greater  neces- 
sity for  their  use,  that  of  providing  access  to  the  sewers, 
should,  however,  have  greater  weight  in  fixing  the  distances 
which  should  separate  them.  It  has  been  found  in  practice 
that  a  6-  or  8-inch  sewer  can  be  easily  inspected  and  cleaned 
if  this  distance  be  not  greater  than  300  feet;  a  12-  or  i8-inch 
sewer,  when  not  more  than  400  feet  separates  successive  man- 
holes. A  sewer  which  can  be  entered  may,  for  this  purpose, 
have  its  manholes  even  600  or  1000  feet  apart;  but  the  cost 
and  difficulty  of  cleaning  are  thereby  increased,  owing  to  the 
distance  the  material  removed  in  cleaning  must  be  carried 
through  the  sewer.  Ventilation  also  is  not  so  well  served  by 
so  great  intervals.  It  is  better  to  fix  500  or  600  feet  as  the 
maximum  distance  between  manholes  on  lines  of  the  largest 
sewers. 

Economy  would  suggest  placing  a  manhole  at  each  sewer 
intersection,  where  it  would  serve  both  lines.  This  is  also 
desirable  as  permitting  a  curved  junction  between  the  sewer- 
channels.  Where  a  curved  bend  is  made  in  the  entire  sewer 
a  manhole  should  be  placed  at  each  end  of  the  curve  unless 
the  sewer  is  sufficiently  large  to  be  entered. 

A  manhole  should  be  placed,  in  general,  at  each  change 


THE  DESIGN.  129 

of  line  or  grade,  in  order  that  every  part  of  the  sewer  may  be 
easily  inspected. 

Economy  will  set  a  limit  to  the  number  of  manholes  which 
may  be  introduced;  the  number  of  the  breaks  in  the  street- 
paving  caused  by  their  covers  it  is  also  desirable  to  keep  at  a 
minimum.  Principally  for  the  first  reason  a  manhole  is  some- 
times omitted  in  small  sewers  when  it  would  come  less  than 
200  feet  distant  each  way  from  another  manhole,  and  a  lamp- 
hole  substituted.  While  the  sewer  cannot  be  inspected  from 
this,  a  light  can  here  be  lowered  into  it  to  light  up  the  sewer 
for  inspection  from  the  next  manhole  either  way.  Lamp- 
holes  have  objectionable  features,  however,  and  are  seldom 
used. 

The  use  of  flush-tanks  has  already  been  discussed  (Articles 
20-22).  The  grades  of  the  laterals  and  the  conditions  of  their 
use  should  be  carefully  examined  to  determine  where  fre- 
quent flushing  will  probably  be  needed.  In  some  cases,  such 
as  where  a  flat  grade  on  a  long  line  of  small  sewer  is  unavoid- 
able, it  may  be  desirable  to  place  automatic  flush-tanks  .at 
intervals  of  800  to  1000  feet  along  its  length,  the  tanks  being 
placed  at  one  side  of  the  sewer  and  discharging  into  it 
through  a  short  connecting-pipe.  If  automatic  appliances  are 
not  employed  no  special  tanks  need  be  built  in  such  a  case, 
but  manholes  at  intervals  along  the  line  can  be  used  for 
flushing. 

All  the  local  conditions  should  be  examined  that  advan- 
tage may  be  taken  of  any  opportunities  for  flushing  offered 
by  springs,  streams,  or  any  available  sources  of  water,  and  in 
general  decision  made  as  to  the  places  and  methods  of  flush- 
ing. As  a  general  rule  every  dead  end  of  a  house-  or  com- 
bined sewer  should  be  flushed  frequently  and  some  arrange- 
ment for  this  placed  at  each  such  point. 

Inlets  should  be  provided  at  frequent  intervals  throughout 
the  area  drained  to  receive  the  surface  water.  In  districts 
where  the  street  traffic  is  considerable  and  where  any  great 


13°  SEWEFAGE. 

depth  of  water  in  the  gutters  would  inconvenience  a  large 
proportion  of  the  population  the  inlets  should  be  not  more 
than  200  or  300  feet  apart,  while  in  residence  districts  they 
may  be  so  situated  as  to  require  the  run-off  to  flow  for  600  or 
700  feet  over  the  surface.  They  should  generally  be  so 
placed  that  all  the  run-off  can  reach  them  by  flowing  along 
the  gutters  only,  and  need  not  flow  across  the  streets.  The 
plan  Plate  V  shows  how  this  can  be  accomplished  in  most 
cases,  Where  this  is  impossible  a  culvert  should  be  placed 
under  the  street-pavement  in  line  with  the  gutter. 

Where  street  grades  are  continuous  from  one  intersecting 
street  to  another  inlets  should  be  placed  on  street-corners. 
They  are  frequently  placed  at  the  gutter  intersection;  but  a 
better  plan  in  many  cases,  particularly  on  steep  grades,  is  to 
place  two  openings,  one  just  above  each  cross-walk,  as  this 
avoids  the  vehicle-trap  caused  by  the  ordinary  corner  inlet. 
Also  an  inlet  should  be  placed  at  every  point  where  two  falling 
grades  meet,  and  if  this  be  between  street  intersections  an 
inlet  must  be  placed  there  on  each  side  of  the  street. 

In  the  majority  of  cities  a  large  proportion  of  the  inlets 
are  provided  with  catch-basins — more  than  the  best  practice 
would  warrant,  in  the  author's  opinion.  The  object  of  using 
a  catch-basin  is  to  retain  there  the  silt  and  other  heavy  matter 
and  not  permit  it  to  be  carried  into  and  deposited  in  the 
sewer.  Catch-basins  should  be  cleaned  after  every  storm. 

The  objection  to  catch-basins  is  that  several  days  some- 
times must  elapse — and  several  weeks  usually  do — between 
the  beginning  of  a  storm  and  the  cleaning  of  the  catch-basin; 
and  during  this  time  the  organic  matter  which  has  been 
washed  or  thrown  into  the  inlet,  including  horse-droppings, 
fruit  and  vegetable  refuse,  etc.,  is  putrefying  and  frequently 
emitting  objectionable  odors.  "  Such  foulness  is  less  offensive 
in  the  drains  [storm-sewers]  than  in  the  catch-basins,  which 
are  situated  at  the  sidewalks  and  where  it  is  much  more 


SHE  DESIGN.  131 

likely  to  be  observed.  Also  it  is  found  impracticable  to 
intercept  all  matter  in  the  catch-basins  which  would  deposit 
in  the  drains  after  they  reach  the  flat  grades  in  the  lower  part 
of  your  city.  The  cleaning  of  the  drains  would,  therefore, 
be  necessary  in  any  event,  and  the  additional  amount  of  silt 
that  would  be  intercepted  by  the  catch-basins  will  not  cost 
much  more  to  remove.  In  the  city  of  Paris,  even  though  a 
combined  system  of  sewers  is  used,  it  is  not  found  objection- 
able to  allow  all  the  street-dirt  to  enter  the  sewers  and  there- 
fore the  catch-basins  at  the  inlets  are  omitted.*'  (Report  of 
Rudolph  Hering  and  Samuel  M.  Gray  on  Sewerage  of  Balti- 
more.) 

As  a  matter  of  fact  catch-basins  are  not  infrequently  left 
uncleaned  after  light  storms,  or  even  heavy  ones,  for  weeks 
together,  and  the  odors  from  them  are  usually  attributed  to 
the  sewers,  which  in  most  cases  are  far  less  foul.  Moreover, 
catch-basins  are  usually  cleaned  with  shovels  only  and  suffi- 
cient filth  left  upon  the  sides  and  bottom  to  become  noticeable 
by  its  odors.  When  cleaned  so  infrequently  the  catch-basin 
often  stands  full  of  material  and  is  until  cleaned  practically 
non-existent  so  far  as  any  useful  effect  is  concerned. 

For  these  reasons  the  universal  use  of  catch-basins  is,  in 
the  author's  opinion,  not  to  be  advised,  but  rather  the  inlet 
should  be  so  designed  that  all  material  shall  at  once  reach  the 
sewer.  The  inlet-connection  he  would  also  make  without  a 
trap,  that  it  may  assist  in  the  ventilation  of  the  sewer;  and  if 
the  sewer  and  its  appurtenances  are  properly  designed,  con- 
structed, and  maintained  there  will  be  very  few  instances 
where  any  odor  can  be  detected  at  the  inlet. 

There  may  well  be  cases  where  catch-basins  are  desirable, 
as  where  the  wash  from  a  steep  hillside  is  caught,  or  for  other 
reason  a  large  amount  of  coarse  soil  or  "  clean  dirt  "  finds  its 
way  to  the  inlet;  and  there  the  catch-basin  will  need  to  be 
large,  that  but  a  small  proportion  of  this  may  reach  the  sewer, 


132  SEWERAGE. 

and  should  be  cleaned  after  every  heavy  shower.     A  small 
catch-basin  is  in  most  locations  worse  than  useless. 

Catch-basins  are  also  desirable  where  the  sewer  grades  are 
very  flat  and  the  velocity  is  less  than  3  feet  per  second ;  also 
on  combined  sewers  where  the  streets  are  unpaved. 

ART.  37.     PUMPING  OF  SEWAGE. 

There  will  frequently  occur  instances  where,  even  if  the 
sewers  be  laid  at  the  flattest  permissible  grades,  either  the 
outlet  will  come  too  low,  or  the  upper  ends  or  some  inter- 
mediate point  will  be  too  high  for  proper  service.  This  is 
especially  likely  to  occur  where  the  outlet  is  at  a  considerable 
distance  from  the  city;  also  where  treatment  of  the  sewage  is 
necessary.  Under  such  circumstances  there  is  but  one  solu- 
tion of  the  difficulty — the  sewage  must  be  raised  at  some  one 
or  more  points  from  a  low  to  a  higher  level.  (Where  a  street 
has  not  yet  been  graded  or  built  upon  it  may  often  be  prac- 
ticable to  lay  the  sewer  above  the  ground-surface  in  crossing 
a  valley  or  basin,  and  so  grade  the  street  finally  as  to  give  it  a 
proper  covering,  thus  avoiding  the  necessity  of  pumping.) 

Where  the  sewage  is  discharged  into  tidal  waters  and  the 
outlet  is  below  high  tide  the  lower  stretch  of  the  sewer  will 
be  filled  twice  a  day,  and  the  velocity  therein  cannot  then 
exceed  the  quotient  obtained  by  dividing  the  volume  of 
sewage  by  the  area  of  the  sewer.  It  would  therefore  be  well 
to  make  this  sufficiently  large  for  present  needs  only  and 
duplicate  it  when  greater  capacity  becomes  necessary.  In 
some  instances  tidal  basins  are  constructed,  which  are  closed 
— automatically  in  most  cases — against  the  rising  tide,  and 
receive  and  hold  the  sewage  flow  during  high  tide,  their  con- 
tents being  discharged  on  the  falling  of  the  tide.  In  some 
cases  the  sewers  themselves  are  made  sufficiently  large  near 
the  outlet  to  serve  as  reservoirs  in  the  same  way.  But  these 


THE   DESIGN.  133 

reservoirs  are  seldom  satisfactory,  owing  largely  to  the  diffi- 
culty of  cleansing  them  from  the  deposits  made  while  they  are 
filled  with  stagnant  sewage.  It  would  be  better,  though  of 
course  more  expensive,  to  pump  the  sewage  during  high  tide; 
or  better  still  to  raise  the  streets  and  sewers  generally,  where 
this  is  possible,  and  discharge  above  high  tide.  (The  city  of 
Chicago,  when  rebuilding  after  the  fire,  raised  the  streets 
over  its  entire  area  to  permit  of  better  drainage). 

In  certain  places  the  conditions  are  such  that  the  water 
rises  above  the  sewer-outlet,  which  is  ordinarily  free,  for 
periods  of  days  or  even  weeks;  as  on  a  lee  shore  during  a 
storm  or  on  rivers  subject  to  extended  floods.  In  such  a 
case  pumping  is  necessary  during  this  period;  but  the  first 
cost  of  the  plant  should  be  kept  at  a  minimum,  since  the 
interest  on  the  saving  in  cost  will  far  exceed  any  saving 
that  could  be  made  in  running-expenses  for  a  few  days.  It 
is  well  to  locate  the  plant  where  power  can  be  obtained 
from  an  outside  source — as  steam  from  the  boilers  of  a 
water- works  pumping-plant,  electricity  from  a  power  or  trac- 
tion company,  etc. — by  which  means  both  first  coct  and 
running-expenses  may  be  reduced. 

Where  house-sewage  only  is  to  be  raised  the  apparatus 
should  be  of  a  capacity  sufficient  for  the  maximum  flow. 
Storm-sewage,  or  at  least  the  entire  run-off  from  heavy 
storms,  is  not  often  pumped,  owing  to  the  enormous  capacity 
required  in  the  machinery.  It  will  in  most  cases  be  found 
more  economical  to  build  special  outlets  for  the  storm-sewage 
to  the  nearest  watercourse,  where  this  is  practicable.  In  the 
case  of  a  combined  sewer  the  house-sewage  should  all  be 
pumped,  as  should  even  the  run-off  from  light  storms,  which 
carries  street-washings.  But  it  will  usually  be  permissible  to 
allow  the  run-off  from  heavy  rains,  with  the  admixture  of 
house-sewage,  to  escape  by  overflows  and  special  storm-sewers 
to  nearer  outlets.  If  this  would  give  rise  to  danger  or  a 
nuisance,  owing  to  even  the  small  proportion  of  house-sewage 


134  -SEWERAGE. 

contained,  it  is  probable  that  the  separate  system  should  be 
employed,  all  house-sewage  being  pumped  and  each  storm- 
sewer  seeking  the  nearest  outlet. 

In  a  very  flat  country  it  may  be  desirable  to  raise  the 
sewage  at  a  great  number  of  points  to  prevent  deep  and 
expensive  excavation.  A  sewer  under  a  level  surface,  begin- 
ning at  a  depth  of  8  feet  and  falling  I  foot  in  300,  would  in 
2100  feet  have  a  depth  of  15  feet.  Beyond  this  the  cost  of 
construction  would  rapidly  increase  unless  the  sewage  could 
be  lifted  and  started  again  at  a  depth  of  8  feet. 

Whether  the  lifting  of  the  sewage  shall  be  done  at  one 
station  or  at  several  is  usually  a  question  of  cost  only.  It 
can  be  exactly  settled  only  by  a  comparison  of  the  sum  of  the 
interest  on  first  cost  and  the  operating-expenses  of  one 
method  as  compared  with  another.  (It  is  assumed  that  the 
depth  of  every  sewer  is  made  sufficient  to  meet  all  require- 
ments.) The  fewer  the  lifting-stations  and  the  further  apart 
they  are  the  greater  will  be  each  lift;  also  the  greater  will  be 
the  average  depth  of  sewer.  Hence,  while  the  greater  the 
distance  between  lifts  the  less  will  be  the  total  cost  of  lifting 
machinery  or  apparatus,  and  also  of  maintenance  of  the  same; 
on  the  other  hand  the  greater  will  be  the  cost  of  the  construc- 
tion of  the  sewer  and  also  of  its  maintenance.  The  proper 
decision  as  to  the  number  and  location  of  the  lifting-stations 
is  frequently  a  problem  requiring  much  careful  study.  While 
in  one  locality,  where  excavation  is  expensive,  5  feet  maybe 
the  maximum  lift  which  will  be  economical,  in  another  this 
limit  may  reach  30  feet  or  more.  If  all  the  lifting  can  be 
done  at  one  or  two  points  it  is  usually  most  economical  to  so 
arrange  it,  even  at  great  expense  for  excavation. 

The  methods  and  apparatus  to  be  employed  may  be: 
pumping  by  steam,  gas,  gasoline,  or  hot-air  engines  or  electric 
motors,  lifting  by  some  pattern  of  automatic  lift  or 
other  appliance  which  seems  adapted  to  the  circumstances. 


THE  DESIGN.  135 

If  steam,  gas,  gasoline,  or  hot  air  be  employed  a  complete 
plant  must  be  placed  at  each  lifting-station.  Where  electricity 
is  the  motive  power  a  motor  and  pump  only  are  required  at  each 
station.  This  renders  possible  a  saving  by  using  electricity, 
under  certain  conditions,  such  as  many  lift -stations  with  a  small 
horse-power  required  at  each,  or  even  when  the  horse-power  is 
considerable.  Improvements  in  electricity  and  low  rates  for  cur- 
rent, combined  with  the  conveniences  of  automatic  action,  have 
led  to  the  adoption  of  electric  plants  for  most  recent  installations 
of  small  and  some  of  large  capacity. 

The  pumps  usually  employed  are  the  piston-  or  -plunger-pump 
and  the  centrifugal  pump.  Other  devices  have  been  employed, 
such  as  screw  and  oscillating  pumps,  but  few  with  any  success. 
The  centrifugal  pump  requires  a  quite  constant  volume  of  sewage 
for  its  proper  working;  hence,  usually,  a  storage-basin,  which  is 
objectionable  but  is  required  in  the  case  of  automatic  pumping 
apparatus.  For  ordinary  lifts  it  is  frequently  more  economical 
than  a  piston-pump;  also  the  wear  due  to  grit  in  the  sewage  is 
neither  so  great  nor  so  injurious  to  the  pump,  and  hence  the  neces- 
sity for  screening  the  sewage  is  not  so  great  as  with  the  piston- 
pump.  With  the  latter  particular  care  should  be  taken  to  re- 
move all  large  solids  and  gritty  matter.  For  this  purpose  gratings, 
wire  screens,  and  settling-tanks  are  employed,  the  last  being  of 
such  cross-section  that  the  velocity  through  them  is  less  than  one 
foot  per  second.  These  should  be  near  or  in  the  pumping-station 
in  order  that  they  may  be  under  the  inspection  of  the  engineer 
and  that  the  deposits  may  be  raised  to  the  surface  by  power.  If 
a  steam-plant  is  used  the  screenings  can  be  burned  on  specially 
prepared  grates. 

The  Shone  Ejector  is  a  device  for  raising  sewage  which  is 
actuated  by  compressed  air.  It  is  usually  employed  where  a 
number  of  lifting-stations  are  needed,  and  the  compressed  air 
for  all  is  supplied  through  iron  pipes  from  one  air-compressing 
station.  While  the  prime  motive  power,  steam,  is  employed 


136  SEWERAGE. 

indirectly,  the  efficiency  of  compressor,  air-pipe,  and  ejector  com- 
bined is  greater  than  if  a  number  of  separate  steam-pumps  are 
used,  with  either  separate  boilers  or  a  central  steam-plant,  espec- 
ially when  the  stations  are  numerous  and  widely  scattered.  For 
only  two  or  three  stations  the  economy  of  their  use  is  doubtful. 

From  none  of  these  lifting  appliances  is  there  any  odor,  under 
good  management.  They  can  therefore  be  placed  at  any  con- 
venient point.  The  small  pumping-plants,  the  Shone  and  other 
ejectors,  are  usually  placed  in  vaults  beneath  the  surface,  the  larger 
plants  above  ground.  The  sewage-pumping  stations  of  Lon- 
don, Berlin,  New  Orleans  and  other  cities  are  within  the  city 
limits,  no  odor  whatever  being  perceptible  near  them. 

A  partial  list  of  the  sewage  pumping  plants  in  this  country 
is  as  follows: 

Electric. — Beverly,  Waltham  and  Lynn,  Mass.;  Olean, 
N.  Y.;  Plainfield,  N.  J.,  electric  air  compressor  and 
ejector;  Charleston,  S.  C;  Albuquerque,  N.  M. 

Steam. — Concord,  Mass.;   Providence,  R.  I.;  Chicago,  111. 

Shone  ejector. — Portsmouth,  Va.;  Winona,  Minn.;  Santa 
Cruz,  Cal. 

Gasoline. — Aberdeen,  S.  D.  (replacing  direct  pressure  from 
an  artesian  well). 

Besides  these,  Woonsocket,  R.  I.;  Buffalo,  Penn  Yan, 
N.  Y.;  Newark,  Summit,  N.  J.;  Washington,  D.  C.; 
Baltimore,  Md. ;  Norfolk,  Va. ;  Brunswick,  Ga. ;  Colum- 
bus, Dayton,  St.  Marys,  O.;  Shelbyville,  Ind.;  E.  St. 
Louis,  111. ;  Manhattan,  Kan. ;  Sioux  City,  la. ;  Houston, 
Tex.;  Salt  Lake  City;  Greenville,  Vicksburg,  Miss.,  and 
Stockton,  Cal.,  pump  sewage,  using  one  or  more  of  these 
methods. 


THE  DESIGN.  137 


ART.  38.    INTERCEPTING-SEWERS  AND  OVERFLOWS. 

It  often  happens  that  a  town  lies  in  a  valley  and  upon  the 
slope  on  one  or  both  of  its  sides,  and  that  while  the  valley 
district  is  too  low  to  sewer  to  the  outlet  by  gravity  the  upper 
districts  are  sufficiently  elevated  to  do  so.  In  such  a  case  it 
would  be  useless  to  carry  all  the  sewage  to  a  main  lying  in 
the  valley  and  raise  it  all  to  a  gravity  outlet-line.  Instead 
a  gravity-main  should  be  run  up  each  side  of  the  valley  at  the 
minimum  grade  to  receive  all  the  sewage  from  higher  up  the 
hill,  leaving  only  the  sewage  from  below  this  to  be  pumped. 
Such  a  main  is  called  an  intercepting-sewer. 

In  some  instances  a  combined  sewer  is  provided  with  an 
outlet  to  the  nearest  watercourse,  which  is  for  storm-sewage 
only,  it  being  intended  that  the  house-sewage  shall  be  received 
and  conducted  away  by  another  sewer,  which  also  is  called  an 
intercepting-sewer. 

This  term  is  also  applied  to  a  long  sewer  which  passes 
down  a  valley  and  receives  the  sewage  from  several  systems 
or  parts  of  systems  to  conduct  it  all  to  a  common  outlet. 

It  is  frequently  advisable,  when  the  gravity-outlet  must 
be  below  high  tide,  to  locate  an  intercepting-sewer  which  can 
discharge  above  all  tidal  influence,  that  the  effect  of  the  seal- 
ing of  the  lower  outlet  may  be  felt  by  only  a  part  of  the 
system,  the  upper  sections  discharging  through  the  free  outlet 
of  the  intercepting-sewer. 

It  sometimes  happens  that  a  system  must  be  extended 
further  in  a  given  direction  than  was  anticipated,  or  that  the 
amount  of  sewage  contributed  by  a  district  becomes  greater 
than  the  sewers  can  carry.  This  can  be  remedied  by  running 
an  intercepting-sewer  across  such  gorged  sewers  at  mid-length, 
intercepting  the  sewage  from  above  and  leaving  the  lower 
lengths  to  carry  only  their  local  sewage. 


138  SEWERAGE. 

Where  storm-water  can  find  near  outlets  from  many  dis- 
tricts  to  a  stream  or  other  body  of  water,  at  which  outlets, 
however,  the  house-sewage  should  not  be  discharged,  an 
intercepting-sewer  may  be  run  along  and  near  the  water  to 
intercept  the  house-sewage  and  convey  it  to  a  satisfactory 
outlet  or  to  a  disposal  grounds  or  works.  By  a  construction 
of  the  sewers  called  an  interceptor  (see  Art.  43)  the  house- 
sewage  and  the  run-off  from  light  rains,  which  is  the  filthiest 
of  storm-sewage,  may  be  diverted  to  the  intercepting-sewer, 
while  the  run-off  from  heavy  storms  will  reach  the  nearer 
outlet.  Mechanical  contrivances  for  diverting  the  sewage  are 
also  used  (see  Art.  43). 

Another  method  of  obtaining  similar  results  is  that  of 
putting  storm-overflows  in  the  combined  sewers,  a  special 
storm-sewer  taking  the  overflow  sewage  to  a  convenient  outlet. 
The  overflow  is,  in  general,  an  opening  in  the  sewer  with  its 
bottom  elevated  some  distance  above  the  sewer-invert.  Until 
the  sewage  reaches  the  height  of  this  overflow  it  remains  in 
the  combined  sewer  and  flows  to  its  outlet;  when  the  quantity 
becomes  such  that  the  height  of  sewage  flow  is  greater  than 
this  the  surplus  discharges  through  the  overflow  into  the 
storm-water  outlet.  It  is  usually  so  arranged  that  this  shall 
occur  only  when  the  dilution  of  house-sewage  by  storm-water 
has  reached  the  point  where  the  discharge  of  the  mixture  into 
a  stream  is  free  from  all  danger. 

With  either  of  these  constructions  the  overflow  or  the 
interceptor  should,  if  possible,  be  at  such  an  elevation  that  it 
cannot  be  reached  by  floods  or  tides  backing  up  the  storm- 
water  sewer. 


THE  DESIGN.  139 

ART.   39.     USE  OF  OLD  SEWERS. 

In  many  cities,  before  any  general  sewerage  system  is  con* 
structed  or  even  thought  of,  short  conduits,  both  private  and 
public,  have  been  built,  discharging  at  the  point  nearest  to 
hand — usually  a  stream  or  lake.  These  are  often  built  in  th$ 
crudest  manner,  graded  by  eye,  and  generally  larger  or 
smaller  than  necessary.  In  other  cases  the  sewers  are  well 
built  and  graded  and  of  a  size  adapted  to  remove  the  storm- 
water,  but  the  outlet  is  located  where  house-sewage  should 
not  be  discharged,  or  the  sewer  is  not  sufficiently  deep  to 
permit  of  receiving  all  house-sewage,  or  it  is  a  pipe  sewer  and 
is  not  provided  with  sufficient  branches  for  house-connections. 
Such  sewers  can  frequently  be  incorporated  into  the  proposed 
system,  and  a  saving  made  of  the  cost  and  the  tearing  up  of 
the  streets  avoided.  But  a  thorough  examination  of  them 
should  first  be  made  to  ascertain  which  ones  can  be  so  used 
and  how. 

If  they  are  sufficiently  large  they  should  be  entered  and 
their  condition  learned  as  to  size,  grade,  character  of  work- 
manship, etc.  If  the  brick-work  is  very  rough  it  may  be 
desirable  to  clean  it  and  plaster  it  with  cement  mortar.  It 
may  be  cleaned  by  washing  first  with  dilute  muriatic  acid> 
then  with  a  solution -of  potash,  and  then  with  water. 

No  connection-pipes  should  be  allowed  to  protrude  within 
the  sewer.  If  the  junctions  are  not  well  designed  they  should 
be  torn  out  and  rebuilt.  If  necessary  a  sufficient  number  of 
manholes  should  be  built  to  bring  the  intervals  between  them 
within  the  proper  limits.  If  it  is  desirable  to  use  an  old  cir- 
cular sewer  as  a  combined  sewer  the  invert  can  be  narrowed 
as  shown  in  Plate  VII,  Fig.  7. 

If  the  sewers  are  too  small  to  be  entered  they  should  be 
examined  thoroughly  from  the  manholes  by  means  of  mirrors 
(Art.  63) ;  pills  (Art.  80)  should  be  passed  through  them  to 


140  SEWERAGE. 

ascertain  whether  the  bore  is  of  uniform  size  and  clear  o! 
deposits.  Their  size,  grade,  elevation,  etc.,  should  be  learned 
by  actual  measurement.  If  they  are  not  laid  in  straight  lines, 
particularly  those  less  than  12  or  15  inches  in  diameter,  it  is 
doubtful  if  they  should  be  used,  unless  manholes  and  lamp- 
holes  can  be  so  judiciously  located  as  to  give  straight  stretches 
of  sewer  between  them. 

If  a  pipe  sewer  is  too  high  for  efficient  service  or  at  too 
flat  a  grade  a  trench  may  be  sunk  along  its  line  and  the  pipe 
taken  up,  cleaned,  and  the  good  ones  relaid  at  a  lower  level 
or  better  grade  in  the  same  trench.  In  the  majority  of  cases 
this  probably  will  be  the  best  disposition  which  can  be  made 
of  old  pipe  sewers.  But  if  it  requires  much  additional  excavation 
to  recover  the  pipes  it  will  be  a  waste  of  money  to  do  so. 

Owing  to  the  difference  in  character  and  volume  of  house- 
and  storm-sewage  a  sewer  not  adapted  for  use  as  a  house  or 
combined  sewer  may  often  be  used  as  a  storm-sewer.  It  fre- 
quently happens  that  old  combined  sewers,  or  even  the  larger 
house-sewers,  are  admirably  adapted  to  this  use,  and  a 
separate  system  can  then  be  built  for  the  house-sewage. 

If  an  old  combined  sewer,  or  storm-sewer  modified  into  a 
combined  sewer  as  explained  above,  can  be  used,  except  that 
the  house-sewage  should  be  discharged  at  a  new  and  more 
distant  outlet,  this  sewage  can  be  discharged  through  an 
interceptor,  or  diverted  by  a  mechanical  regulator  into  an 
intercepting  house-sewer,  and  the  old  outlet  used  to  discharge 
the  storm-water  only. 

But  the  efficiency  of  the  system  is  of  greater  moment  than 
small  economies,  or  even  large  ones,  and  should  not  be  sacri- 
ficed to  them. 


CHAPTER   VII. 

DETAIL   PLANS. 

ART.  40.     THE  SEWER-BARREL. 

SEWERS  have  been  made  of  almost  every  conceivable 
shape  and  the  walls  built  of  all  kinds  of  materials.  A  few 
shapes  and  materials  are  of  almost  universal  applicability, 
others  are  adapted  to  peculiar  circumstances  only,  and  some 
are  freaks  of  invention  adapted  to  no  circumstances. 

The  shape  of  cross-section  is  to  a  certain  extent  controlled 
by  the  material  of  which  the  sewer  is  constructed.  The 
smallest  sewers  cannot  be  advantageously  built  of  brick,  but 
are  usually  composed  of  earthenware  or  metal  pipes  or  of 
cement.  Earthenware  sewers  are  made  from  2  to  42  inches 
interior  diameter.  They  are  seldom  made  other  than  circular, 
owing  to  the  liability  of  other  shapes  to  become  distorted  in 
burning.  Metal  pipes  are  employed  where  the  sewer  will  be 
under  pressure,  as  in  a  siphon,  or  where  there  is  a  great  deal 
of  ground-water;  also  sometimes  to  better  resist  disturbing 
forces,  as  in  made  or  treacherous  ground  or  outlets  under 
water  or  in  shifting  sands.  The  only  metal  commonly  em- 
ployed is  iron.  Metal  pipes  have  always  been  made  circular, 
although  there  are  none  but  economic  reasons  why  other 
forms  could  not  be  made. 

Concrete  and  cement  sewers  are  made  of  all  sizes  and  shapes — 
circular,  egg-shaped,  rectangular,  etc.  Concrete  is  used  for  both, 
but  the  particles  of  the  aggregate  for  the  smaller  are  so  fine  as  to 
make  it  practically  coarse  mortar,  and  these  are  called  cement 
sewers.  141 


142  SEWERAGE. 

Wooden-stave  sewer-pipe  has  been  used  in  the  West,  uid 
in  the  East  to  some  extent.  On  the  Los  Angeles  outfall 
sewer  are  34,100  feet  of  36-  and  38-inch  pipe  of  this  descrip- 
tion. The  outlet  sewers  in  New  York  and  Brooklyn  are  many 
of  them  creosoted  wooden-stave  pipe  of  3  or  more  feet 
diameter. 

For  all  sewers  the  circle  is  the  most  economical  shape,  and 
generally  the  most  desirable,  if  they  are  never  to  run  less  than 
-|  full,  except  that  the  use  of  platform  foundations  may 
modify  the  first  statement.  But  if  they  are  to  be  used  as 
combined  sewers  the  egg  shape  is  to  be  preferred,  or  a  form 
similar  to  Plate  VII,  Figs.  2  and  6. 

In  Brooklyn,  N.  Y.,  and  a  few  other  cities  cement  sewer- 
pipe  has  been  used,  and  in  general  all  sizes  of  this  above  1 2  inches — 
in  Brooklyn  all  sizes — are  egg-shaped.  Sections  of  this  pipe 
are  shown  in  Plate  VI,  Figs.  I  and  2.  The  flat  base  is  given 
the  pipe  to  prevent  its  rolling  in  the  trench  after  being  placed 
in  position  and  to  strengthen  the  bottom  against  crushing. 

In  the  case  of  large  sewers,  particularly  those  whose 
diameter  exceeds  4  or  5  feet,  it  frequently  becomes  necessary 
to  make  the  width  greater  than  the  height,  because  the  depth 
of  the  invert  is  limited  by  sewer-grade  requirements  and  the 
height  of  the  arch  by  the  street  grade.  A  great  number  of 
shapes  have  been  designed  to  meet  these  conditions.  Some 
of  the  best  are  shown  in  Plate  VI,  Fig.  5,  and  Plate  VII, 
Figs.  9  and  10.  Plate  VII,  Fig.  4,  shows  a  design  for  very 
low  head-room,  but  the  thrust  of  the  arch  is  considerable  and 
the  side  walls  should  be  heavier  than  shown  unless  they  are 
firmly  backed  by  rock  or  solid  earth.  Plate  VIII,  Fig.  I,  is 
a  better  design  to  employ  where  the  head-room  can  be 
slightly  increased. 

The  use  of  steel  beams  for  supporting  the  roof,  with 
vertical  side  walls,  as  shown  in  Plate  VII,  Figs.  9  and  10,  is 
becoming  quite  common,  and  is  probably  the  best  construe- 


DETAIL   PLANS.  143 

tion  for  soft  ground  with  limited  head-room.  Fig  10  is 
adapted  to  storm-water  only,  or  to  a  flow  of  house-sewage 
never  less  than  15  inches  deep.  The  egg-shaped  sewer  in 
Fig.  9  is  intended  for  the  house-sewage,  the  larger  channels 
for  storm-water. 

Plate  VIII,  Figs.  2  and  3,  show  substitutes  for  egg-shaped 
sewers  where  the  head-room  is  contracted.  In  Fig.  3  the 
semicircular  invert  should  be  sufficiently  deep  to  admit  of 
carrying  the  maximum  house-sewage  flow,  that  the  sloping 
benches  may  not  be  fouled  by  it.  Fig.  2  is  especially  adapted 
to  an  exceedingly  variable  house-sewage  flow,  as  from  a  fac- 
tory district  whose  Sunday  and  holiday  flow  is  inconsiderable. 

Plate  VI,  Figs.  5  and  9,  Plate  VII,  Figs.  4,  5,  and  10, 
and  Plate  VIII,  Fig.  I,  are  best  adapted  to  storm-sewage 
only,  although  they  may  be  used  as  combined-sewer  mains  if 
the  depth  of  the  house-sewage  flow  is  never  less  than  4  to  6 
inches  at  the  shallowest  part,  and  the  velocity  is  then 
sufficient.  Plate  VI,  Figs.  I,  6,  7,  and  8,  are  intended  for 
house-'sewage  only.  In  Fig.  7  the  flat  invert  is  permissible 
owing  to  the  constant  depth  of  the  sewage  flow,  which  con- 
sists of  intercepted  house-sewage  from  a  number  of  residence 
suburbs. 

Plate  VI,  Figs.  2  and  3,  Plate  VII,  Figs.  1,2,  3,  6,  7, 
and  9,  Plate  VIII,  Figs.  2  and  3,  are  intended  to  act  as  com- 
bined sewers.  In  Plate  VII,  Figs.  5  and  6,  the  side  bench  is 
horizontal,  that  it  may  serve  as  a  sidewalk  for  sewer  inspectors 
and  cleaners. 

The  circular  or  egg-shaped  form  demands  for  strength  a 
solid  support  under  its  invert.  Where  the  soil  is  clay  or  firm 
loam,  or  a  mixture  of  these  with  sand  or  gravel,  or  rock  easily 
shaped,  such  a  sewer  may  be  built  with  walls  of  uniform 
thickness,  the  invert  bearing  upon  ground  shaped  to  receive 
it.  If  the  ground  is  not  firm,  however,  or  cannot  be  readily 
shaped,  the  sub-invert  spaces  must  be  filled  with  concrete, 


144 


SEWERAGE. 
Plate  VI. 


FIG.  3. 

IN  SOFT  EARTH  IN  FIRM   EARTH 

BRICK    SEWER 


TIG.  6. 

INTERCEPTING  Sb'WF.R  AND 
SUB-DKAIN.  BALI  IMORE,  MD. 


RG-7-     IN  <^»  TUNNEL 

METROPOLITAN  SEWERS  (BOSTON) 


MOCK 

EXCAVATION 


SPECIAL  SECTION  BENEATH  RAILWAY* 

FIG.  8.  SALT  LAKE  CITY. 

OUTLET  SEWER, 


FIG.  9.  FIG.  10. 

Y?B8T  SIDE  TRUNK  SEWER,  ROCHESTER. 


DETAIL   PLANS.  145 

brick,  or  stone  masonry,  as  in  Plate  VI,  Figs.  ?,  5,  6,  8, 
and  9.  If  the  arch  is  of  such  dimensions  that  the  horizontal 
thrust  becomes  more  than  the  soil  can  receive  without  yield- 
ing, then  the  side  walls  must  be  designed  to  receive  this 
thrust,  as  in  Plate  VI,  Figs.  5,  6,  8,  and  9.  The  general 
principles  of  arches  apply,  of  course,  to  arched  sewers,  one  of 
the  most  important  being  the  necessity  for  stiffness  of  the 
haunches. 

The  circle,  as  has  been  stated,  is  the  most  economic  shape 
for  a  sewer  when  the  invert  requires  no  backing.  When  this 
is  necessary,  however,  the  circle  becomes  an  expensive  shape, 
and  the  most  economic  is  one  with  vertical  side  walls  and 
bottom  flat  or  conforming  generally  to  the  shape  of  the  trench 
bottom.  This  is  seen  by  an  inspection  of  Plate  VI,  Figs.  6 
and  8,  Plate  VII,  Figs,  4  and  10.  It  is  for  this  reason  that 
most  of  the  flat-bottomed  sewers  are  built.  Permanency  of  con- 
struction demands  a  covering  for  timber  platforms,  which  are 
liable  to  abrasion  and  also  to  rotting  away  if  exposed  as  the  sewer 
bottom.  This  covering,  forming  the  sewer  bottom,  is  usually 
given  a  curved  form,  as  in  Plate  VI,  Fig.  5,  or  a  sloping  one,  as 
in  Plate  VIII,  Fig.  i,  for  two  reasons*  to  concentrate  small  streams 
and  decrease  deposits,  and  to  give  strength  to  the  bottom  to  resist 
the  upward  pressure  which  will  exist  when  the  soil  is  soft  mud, 
quicksand,  or  similar  material. 

The  materials  of  which  sewers  are  commonly  composed 
are  brick,  stone,  and.  concrete  masonry,  cement  and  vitrified 
salt-glazed  pipe,  and,  under  special  conditions,  cast-  or  wrought- 
iron  or  steel  pipe. 

Stone  and  brick  masonry  is  usually  built  up  in  cement  mortar, 
and  cement  is  always  used  for  concrete.  The  stone  masonry 
is  usually  rough,  but  compact  and  well-built,  rubble.  In  arches 
brick  is  usually  employed  rather  than  stone,  as  being  cheaper  and 
also  stronger  unless  the  stone  are  carefully  dressed.  The  interior 
surface  of  the  sewer,  when  this  is  built  of  stone,  is  usually  lined 


146 


SEWERAGE. 


Plate  VII. 


STONt  MASONBY 


STCNE  MASONRY 


J^ETE  /  FIG.  4.    TIBER  CREEK, (WASHINGTON) 

SEWER  IN  1893. 
FIG.  1.  FIG.  2.  FIG.  3. 

WASHINGTON  D.C.       STANDARD  SEWERS. 


FIG.  6.     NEW  STYLE.        FIG.  7.     OLD   LONDON  SEWER. 
WITH  IMPROVED  INVERT. 


FIG.  9.     DOUBLE  STORM  CHANNEL  AND  HOUSE  SEWER;  BRUSSELS.         FIG.  8.     OLD  LONDON  "SEWER 
UNDER  RAILWAY  TRACKS.  OP  DEPOSIT." 


3JCONCRETE  ANOJ  PLASTERING 


;u  U  U  U 

FIG.  10.      CANAL  STREET  SEWER;    ST.  PAUL,  MINN. 


DETAIL   PLANS.  147 

with  a  4-inch  ring  of  brick,  because  a  brick  surface  can  be  more 
easily  made  smooth  than  can  stone  masonry  (see  Plate  VI,  Fig. 
9).  If  much  wear  is  anticipated  smooth-dressed  granite  or  trap 
blocks  or  hard  paving  brick  are  frequently  used  as  invert-lining 
(see  Plate  VI,  Fig.  8). 

Where  the  foundation  is  yielding  a  concrete  base  is  fre- 
quently used  under  the  sewer,  as  in  Plate  VI,  Fig.  8,  Plate 
VII,  Fig.  9.  But  if  it  is  soft  a  platform  or  even  piles  should 
be  used  under  the  concrete. 

If  arches  of  small  radius  are  built  of  brick-work  laid  with 
radial  joints  much  cement  is  used,  the  arch  is  often  weak,  and 
the  inner  surface  a  polygon  in  section  rather  than  a  curve, 
unless  brick  especially  shaped  are  used.  If  laid  well  such 
arches  are  also  expensive  in  labor.  To  meet  these  objections, 
which  apply  particularly  to  inverts  in  egg-shaped  brick  sewers, 
invert-blocks^  oTvitrified  clay  have  been  used.  There  are 
objections  to  these,  the  principal  of  which  is  that  a  joint 
entirely  through  the  sewer  is  made,  and  where  the  hydrostatic 
head  is  greatest,  which  is  almost  sure  to  permit  the  leakage  of 
water  into  or  out  of  the  sewer.  They  are  also  rather  expen- 
sive, and  are  but  little  usqd,  now.  A  section  of  such  a  block 
is  shown  in  Plate  VI,  Fig.  I  n- 

A  better  plan  for  constructing  short-radius  inverts  is  by 
the  use  of  concrete  or  brick,  lined  on  the  inside  with  vitrified 
sewer-pipe  split  into  thirds,  which  is  approximately  the  arc  of 
the  small  invert-circle  in  the  egg-shaped  sewer.  Such  a  con- 
struction is  shown  in  Plate  VIII,  Fig.  2.  This  construction 
is  also,  well  adapted  to  such  sewers  as  are  shown  in  Plate  VII, 
Figs.  2,  6,  and  7,  Plate  VIII,  Fig.  3. 

Whole  vitrified  pipe  are  used  for  lining  to  circular  sewers 
up  to  42  inches  diameter,  when  the  pipe  is  not  used  alone  on 
account  of  the  additional  strength  or  tightness  of  joints 
required. 

Concrete  is  being  used  extensively  for  sewers  of  24  inches 


148 


SEWERAGE. 
Plate  VIII. 


STEEL  I   BEAM 


FIG.   1. 


STEEL  T  BEAM 


I'SOLT 


FIG.  4. 

WOODEN  OUTLET  SEWER 
NEW  YORK  CITY, 


8TEEL  I  BEAM 


I  A-B. 

FIG.  5.  JUNCTION  MANHOLE. 


flG.7.  JUNCTION  OF  BRICK  SEWE8S. 


SECTIONAL  PLAN 

FIG.  6.  JUNCTION  OF  8  FT.  AND  1 1  FT.  SEWERS. 


FIG   8.  FIG   9. 

HUB  &  SPIGOT  JOINT,  RINQ  JOINT. 


FIG    10.  ,, 

BEVEL  JOINT.  ARCHER     JOlNTf, 


DETAIL  PLANS. 


149 


diameter  and  larger,  and  of  all  shapes.  Perhaps  the  majority 
are  either  round  or  "horseshoe,"  " basket-handle "  or  similar 
shape.  A  great  many,  especially  of  the  larger  sizes,  are  rein- 
forced with  steel  rods,  coarse  wire  screen  or  expanded  metal. 

Concrete  pipe  two  to  five  feet  in  diameter  is  used  in  many 
cases  instead  of  depositing  the  concrete  in  place;  the  pipe  being 
generally  made  along  or  near  the  trench.  It  is  frequently  rein- 
forced (there  are  three  or  four  patented  styles  of  reinforced  pipe) 
and  generally  contains  a  mixture  of  one  part  cement  and  about 


Bell  and  spigot  ends  shown  separately  and  also  when  placed  together. 
FIG.  5. — JOINT  OF  A  "  LOCK  JOINT  "  REINFORCED  CONCRETE  PIPE. 

three  of  sand  and  grit  and  three  of  f-inch  stone.  One  patented 
style  is  built  of  four  segments  or  voussoirs,  made  in  moulds  and 
reinforced. 

Concrete  possesses  the  advantage  over  brick  that  it  does  not 
require  skilled  labor,  and  is  generally  cheaper;  and  it  can  be 
made  to  any  desired  form  by  using  the  necessary  forms  and 
centres.  When  well  made  it  is  equal  if  not  superior  to  the  best 
hard-burned  sewer  brick  in  resistance  to  abrasion  in  inverts. 
Concrete  inverts  at  Duluth  twenty  years  old  show  no  appreciable 
wear  under  conditions  which  made  it  necessary  to  renew  brick 
inverts  in  six  or  seven  years.  But  the  invert  should  be  of 


150  SEWERAGE. 

rich  mortar — about  i  :  i — well  mixed  and  troweled  down 
smooth. 

There  is  no  fixed  rule  for  the  thickness  of  sewers,  which  de- 
pends upon  the  shape  and  diameter  of  bore,  the  material,  the 
pressure  received  from  the  surrounding  soil,  and  other  circum- 
stances. Brick  sewers  less  than  30  inches  diameter  are  fre- 
quently made  but  one  ring — 4  inches — thick;  from  this  up  to 
about  60  inches,  2  rings  or  8  inches  thick;  from  this  up  to  120 
inches,  3  rings  or  12  inches  thick.  This  applies  to  the  arch 
more  particularly,  unless  the  surrounding  ground  is  very  firm, 
when  the  invert  may  be  made  of  equal  thickness,  or  even  8  inches 
thick  only  when  the  arch  is  12  inches  or  more  thick.  Some 
engineers  never  use  less  than  two  rings  of  brick  in  a  sewer-arch; 
some  use  one  ring  up  to  diameters  of  3  feet  or  more.  The 
latter  may  give  sufficient  strength  against  crushing,  but  is  hardly 
stiff  enough  to  resist  distortion  except  under  unusually  favorable 
circumstances. 

The  thickness  of  the  side  walls,  when  these  are  vertical,  must 
be  such  as  to  enable  them  to  withstand  the  pressure  of  the  soil 
without  or  of  the  water  within  the  sewer  when  it  is  full;  also 
to  receive  the  thrust  of  the.  top  arch  when  the  soil  is  not  capable 
of  doing  so.  For  the  thickness  of  concrete  walls  there  seems 
to  be  no  recognized  standard  rule.  Mr.  Wm.  B.  Fuller's  rule 
is:  For  crown  and  invert  ^d  +  i  inch;  for  haunches,  i^  times 
crown;  with  a  minimum  of  3  inches  for  crown  and  6  for  invert 
and  haunches. 

Of  fifteen  different  designs  in  1909  four  followed  the  above 
rule;  five  had  the  thickness  TV  the  diameter;  one  A +3  inches; 
one  -f4-;  one  ^;  one  i;  and  two  J.  One  make  of  reinforced 
concrete  pipe  has  a  thickness  ^  the  diameter  +  2$-  inches. 

Mr.  C.  D.  Hill,  chief  engineer  of  sewer  construction  of  Chicago, 
uses  the  formula^o^SV^+o.i  ft.;  which  gives  approximately 
m-  UP  t°  6  ft.;  8  in.  for  8  ft.  and  9  in. for  n  ft. 

In  general,  reinforced  concrete  sewers  are  made  as  thick  as 


DETAIL  PLANS.  151 

those  not  reinforced,  and  Frederick  W.  Taylor  says  (in  "Con- 
crete, Plain  and  Reinforced")  "The  use  of  steel  reinforcement 
is  not  usually  advisable  under  ordinary  conditions,  because  of 
the  cost  and  the  difficulty  of  properly  placing  the  metal."  The 
cost  of  the  steel  in  most  cases  might  better  be  placed  in  additional 
concrete,  unless  the  sewer  is  to  be  under  internal  pressure. 

When  two  sewers  intersect,  one  or  both  should  be  curved 
in  the  direction  of  flow  of  the  other.  If  one  or  both  are  small, 
the  curve  may  be  made  in  a  manhole  (Plate  VIII,  Fig.  5). 
If  one  is  many  times  larger  than  the  other,  the  curve  may  be 
omitted,  the  branch  making  an  angle  of  45°  with  the  main  sewer 
at  the  junction.  Where  they  are  each  larger  than  30  to  36 
inches  diameter  the  intersection  should  be  made  by  bringing 
the  two  barrels  gradually  into  one.  This  will  require  con- 
siderable skill  in  both  design  and  construction  when  the  tops 
and  inverts  are  both  arched.  When  the  top  is  a  girder  con- 
struction the  plan  is  much  simplified,  and  still  more  so  if  the  bot- 
tom also  is  flat.  The  crown  of  the  sewer  a  short  distance  be- 
low the  junction  should  be  as  low  as  that  of  the  lower  of  the  two 
sewers  a  few  feet  above  it.  A  plan  of  a  junction  of  two  cir- 
cular sewers  is  shown  in  Plate  VIII,  Fig.  6,  and  another  in  Fig. 
7  with  I-beam  roof  construction  for  supporting  heavy  loads  or 
where  the  head  room  is  limited. 

ART.  41.    PIPE  SEWERS. 

Pipe  is  ordinarily  used  for  sewers  up  to  20  or  even  30  inches 
diameter.  Above  this  up  to  42  inches  vitrified  clay  pipe  is 
sometimes  used,  but  many  engineers  are  doubtful  of  the  strength 
of  the  larger  sizes  against  crushing.  The  smaller  sizes  up  to  18 
or  24  inches,  when  made  of  good  clay  well  burned,  are  sufficiently 
strong  for  ordinary  locations,  although  the  "double-strength" 
pipe  (having  a  thickness  of  shell  ^  the  diameter)  is  recommended 
rather  than  those  of  the  standard  thickness,  which  is  less  than 
-j-y  the  diameter  by  a  difference  which  increases  with  the  diameter. 


152 


SEWERAGE. 


It  is  probable  that  if  this  thickness  be  maintained  the  largest 
sizes  of  pipe  are  amply  strong  for  ordinary  circumstances. 

In  many  instances  where  vitrified  clay  pipe  has  been 
crushed  in  the  ground  it  has  been  found  that  this  was  probably 
due  to  the  fact  that  the  pipe  had  a  bearing  on  the  bottom  at 
only  one  or  two  points  instead  of  along  its  entire  length,  or 
that  stones  or  frozen  earth  were  thrown  upon  it  in  back-filling. 
If  earth  is  well  tamped  under  and  around  a  vitrified  clay  pipe 
it  will  not  usually  collapse,  even  when  broken,  although  it 
may  leak.  Such  pipe  ordinarily  breaks  along  four  lines — at 
top,  bottom,  and  each  side — into  pieces  of  almost  equal  size. 
For  this  reason  fire-cracks  and  slight  imperfections  which  do 
not  cause  the  rejection  of  a  pipe  should  be  placed  at  a  point 
about  45°  above  the  horizontal  in  laying,  and  not  at  the  top. 

Several  tests  have  been  made  of  the  strength  of  vitrified 
clay  pipe.  In  one  series,  in  which  the  pipe  were  bedded  in 
sand  and  the  load  applied  to  the  entire  length  of  the  top, 

8-inch  pipe  broke  when  the  weight  per  foot  of  length  was  1363  to  2256  pounds 
I2     ••       •«         "         «•        "         ••        "       "     "       "         ••     1227102756 
15     "       "         '«          "        "         "        "      "     "       "         '•    1261  to  2297       " 
18     "       "         "         "        "         "        "       "      "       "         "     1464102093       " 

From  similar  tests  made  in  1897  F.  A.  Barbour  of  Boston 

/i.6S 

deduced  the  expression  /  =  c—r  ,  in  which  /  is  the  pressure 

per  lineal  foot  in  pounds  at  the  first  cracking,  t  is  the  thick- 
ness in  inches,  d  is  the  diameter  in  inches,  and  c  =  33,000. 

Tests  made  by  T.  H.  Barnes  on  the  strength  of  12 -inch 
vitrified  clay  pipe  when  acting  as  a  beam  between  supports  2 
feet  apart  gave  the  following  results: 


Thickness. 

Cracked  at 
(Pounds) 

Broke  at 
(Pounds) 

Equal  to 
(Lbs.  per  Lin.  Ft.) 

Remarks. 

' 

IIOO 

2750 

i860 

Fire-crack 

' 

2OOO 

2OOO 

1330 

/ 

2690 

2810 

1870 

' 

2220 

2450 

1630 

/ 

91  IO 

2535 

1690 

DETAIL  PLANS. 


153 


The  Borough  of  Brooklyn,  New  York,  maintains  a  pipe- 
testing  laboratory,  and  tests  all  pipe  used  on  city  work.  These 
tests  have  been  carried  on  since  1906,  during  which  time  many 
hundred  have  been  made.  They  consist  of  external  crushing, 
internal  hydrostatic  pressure  and  drop-weight  tests.  Branches 
or  spurs  also  are  tested,  to  determine  whether  they  are  firmly 
attached  to  the  pipe. 

The  crushing  test  is  made  by  bedding  the  pipe  in  a  box  of 
sand  and  applying  pressure  by  a  Reihle  machine,  a  strip  of  hard 
wood  bearing  along  the  full  length  of  the  top  of  the  pipe  being 
used  to  transmit  the  pressure,  plaster  of  paris  being  placed  be- 
tween the  pipe  and  this  strip.  Of  over  1,000  pipes  tested,  the 
average  pressure,  in  pounds  per  linear  foot,  required  to  break 
each  of  several  sizes  of  pipes,  together  with  the  lowest  and  highest 
results,  were  as  follows: 


Pressure,  in  Pounds  per  Linear  Foot  of  Pipe,  required  to  crush 

Vitrified  Clay  Pipe. 

Size, 

Inches. 

Average. 

Highest. 

Lowest 

Required  by 
Specifications. 

6 

4,275 

7,167 

2,128 

J,OOO 

9 

3,983 

4,845 

2,852 

1,050 

12 

4,696 

7,144 

2,244 

1,15° 

15 

5,046 

6,755 

3,218 

1,300 

18 

6,311 

12,211 

3,23° 

1,45° 

24 

9,866 

14,239 

7,780 

2,000 

Cement  pipe  tested  in  1909  showed  average  crushing  pres- 
sure per  linear  foot  as  follows:  1 2-inch  circular  pipe,  2  years  old, 
1,983  pounds;  i  month  old,  1,689  pounds.  1 2-inch  egg  shape, 
i  year  old,  1,911  pounds.  15-inch  egg-shape,  i  year  old,  1,962 
pounds;  i  month  old,  1,800.  i8-inch  egg-shape,  2  years  old, 
1,978  pounds;  i  month  old,  1,767. 

Impact  tests  were  made  by  dropping  a  lo-pound  ball  from 
various  heights  onto  one  spot  on  a  sewer  pipe  until  it  cracked. 
The  specifications  call  for  a  fall  of  18  inches,  and  at  least  two 


154  SEWERAGE. 

blows.  Under  this  test,  in  1909,  1 8-inch  vitrified  clay  pipe  re- 
ceived 2  to  98  blows;  i5-inch,  6  to  7  blows;  1 2-inch,  2  to  4  blows; 
6-inch  pipe  all  broke  at  the  first  blow.  Complete  failure  required 
from  2  to  200  blows,  combining  all  sizes. 

The  hydrostatic  test  is  seldom  used,  practically  all  vitrified 
pipe  successfully  resisting  the  specified  pressure  of  33  pounds 
per  square  inch. 

The  exact  amount  of  pressure  brought  to  bear  upon  a 
sewer  by  back-filling  is  uncertain.  For  a  few  feet  of  depth  it 
probably  bears  the  entire  weight  of  the  earth  immediately 
above  it.  With  granular  material  the  proportion  of  pressure 
to  weight  of  back-filling  probably  decreases  but  little,  while 
with  other  soils  it  decreases  more  or  less  rapidly  after  the 
depth  equals  the  width  of  the  trench.  But  it  is  probable  that, 
while  the  latter  material  gives  an  almost  vertical  pressure,  the 
former  acts  more  as  a  fluid,  pressing  normally  to  the  surface 
of  the  sewer,  and  is  not  so  liable  to  crush  it.  Little,  however, 
is  known  on  this  point.  From  certain  experiments  in  which 
natural  conditions  were  only  partially  reproduced  it  was 
thought  probable  that  for  trenches  10  feet  or  more  deep  the 
percentage  of  weight  of  back-filling  transmitted  to  the  sewer 
equalled  I  —(coefficient  of  friction  of  the  material);  that  gravel 
transmits  36  per  cent  and  wet  clay  65  per  cent  of  its  weight; 
that  up  to  10  feet  the  percentage  transmitted  decreased  from 
100  per  cent  as  the  square  or  cube  of  the  depth.  If  the 
depth  of  covering  is  small  there  is  danger  that  outside  weight 
from  road-rollers  or  even  heavy  wagons  may  crush  it.  But 
this  danger  appears  to  be  very  slight  when  the  depth  of 
covering  equals  or  somewhat  exceeds  double  the  width  of 
trench. 

The  joints  of  vitrified  clay  pipe  sewers  are  generally  made 
of  the  bell-and-spigot  pattern,  as  shown  in  Plate  VIII, 
Fig.  8.  The  ring-joint  (Fig.  9)  is  not  now  very  extensively 
used,  as  its  supposed  advantages  are  found  to  be  largely 


DETAIL   PLANS.  155 

imaginary,  while  its  disadvantages  are  not.  It  is  almost  im- 
possible to  make  tight  joints  with  the  ordinary  ring-joint  and 
the  expense  is  greater. 

The  joint  of  a  bell-and-spigot  pipe  is  made  sometimes  of 
clay,  but  in  this  country  cement  mortar  is  almost  universally 
used.  Clay  has  cheapness  alone  to  recommend  it  as  compared 
with  cement.  Other  materials  have  been  used  for  sewer-pipe 
joints,  such  as  the  Stanford  preparation,  a  tar-and-sulphur 
compound.  In  Germany  asphalt  has  been  used  for  some  years 
and  good  results  reported.  Sulphur  and  sand  has  been  used  in 
Newark,  N.  J.;  and  pitch  pine  tar  and  cement  kneaded  together, 
in  Atlantic  City.  Most  of  these  materials  are  more  ex- 
pensive and  less  durable  than  Portland  cement,  and  are  prob- 
ably to  be  preferred  to  it  only  under  certain  circumstances, 
if  at  all. 

A  glazed  clay  pipe  offers  a  poor  surface  for  cement  to  ad- 
here to,  and  consequently  with  it  an  absolutely  tight  joint  is 
very  difficult  of  construction;  but  if  faithful  care  be  taken  with 
each  joint  a  practically  tight  sewer  is  possible.  But  such  sewers 
are  rare.  After  a  short  period  of  use,  however,  a  fairly  good 
cement  joint  will  become  so  stopped  with  matter  strained  from 
outfiltering  sewage  as  to  be  practically  water-tight.  But  if  the 
head  of  ground-water  is  greater  than  that  of  sewage  the  flow 
will  be  inward  and  the  joint  will  probably  not  become  tighter 
than  it  was  at  construction.  Under  such  conditions  special 
precautions  should  be  taken,  such  as  surrounding  each  joint 
with  concrete. 

If  much  sewage  leaks  out  through  a  joint  there  is  danger  that 
the  remaining  fluid  will  not  be  sufficient  to  keep  the  sewer  clean 
of  deposits.  But,  as  just  stated,  such  a  condition  seldom  con- 
tinues for  a  long  time  after  the  sewer  is  put  into  use  if  the  joints 
were  well  made. 

Several  modifications  of  the  ordinary  joint  have  been  de- 
signed to  overcome  this  difficulty,  such  as  grooving  the  outside 


156  SEWERAGE. 

of  the  spigot  end  and  the  inside  of  the  bell.  One  style  of  patent 
joint  is  shown  in  Plate  VIII,  Fig.  n.  Such  complicated  joints 
are  expensive  and  difficult  both  to  manufacture  and  to  lay,  and 
are  seldom  used.  If  there  is  considerable  ground-water  it  is 
better  to  lay  the  pipe  as  shown  in  Plate  VII,  Fig.  3,  or  to  use 
light-weight  or  second-quality  cast  iron,  or  wrought  iron  or  steel. 
Carefully  made  concrete  or  brick  sewers  may  also  be  used  for  the 
larger  sizes,  of  extra  thickness  to  resist  percolation,  or  water- 
proofed with  layers  of  tar  paper  or  with  a  surface  coat  of  water- 
proofing compound. 

The  amount  of  ground-water  which  may  leak  through  a 
cement  joint  depends  very  largely  upon  the  shape  of  the  bell 
and  the  manner  in  which  the  joint  is  made.  If  the  annular 
cement-space  in  the  bell  is  too  small  the  cement  is  likely  to 
be  improperly  compacted  therein  or  not  to  enter  at  all  at 
some  points.  Experiments  seem  to  show  that  the  deeper  the 
ring  of  cement  in  this  joint  the  less  the  leakage.  If  for  any 
reason  the  cement  draws  away  from  either  bell  or  spigot  a  leak 
is  caused.  Hence  it  seems  best,  particularly  in  wet  soils,  to 
use  extra  deep  and  wide  sockets.  The  present  standard  of 
width  is  |  inch  for  pipe  from  4  to  10  inches  diameter  and  J  inch 
from  12  to  24  inches  diameter;  but  "deep  and  wide  socket" 
pipe  are  made  having  f-inch  space  for  all  sizes,  from  5  to  24-inch. 
The  depth  of  socket  on  "standard  pipe"  varies  from  ij  inches 
on  2 -inch  pipe  to  3^  inches  on  24-inch.  "Deep  and  wide  sock- 
ets" are  from  J  to  J-inch  deeper,  and  are  to  be  preferred,  in  our 
opinion. 

With  poor  joints  the  amount  of  leakage  may  be  limited 
only  by  the  amount  of  ground-water,  but  with  the  best  of  cement 
joints  in  very  wet  ground  the  leakage  may  amount  to  5000  to 
20,000  gallons  per  day  per  mile  of  sewer.  In  very  many  systems 
it  is  more  than  ten  times  this  amount. 

/  Experiment  seems  to  show  that  neat  Portland  cement  makes 
[the  tightest  joints,  Portland  cement  and  sand  i  :  i  the  next, 


DETAIL  PLANS.  157 

natural  cement  and  sand  i  :  i  the  next  and  natural  cement  neat 
the  most  porous  joint. 

Since  the  joint  is  the  weak  place  in  a  pipe,  the  fewer  joints 
there  are  the  better.  The  expense  of  laying,  also,  is  decreased 
by  decreasing  the  number  of  joints.  For  these  reasons  the  use 
of  3-foot  rather  than  2-foot  lengths  of  pipe  is  advised.  Vitri- 
fied clay  pipes  more  than  3  feet  long  have  not  as  yet  been  manu- 
factured with  success,  but  3-foot  lengths  can  be  furnished  by 
most  pipe-manufacturers  as  the  same  price  per  foot  as  the  2-foot 
lengths.  Some  prefer  to  use  the  2-foot  lengths  when  the  diam- 
eter of  the  pipe  exceeds  15  or  18  inches,  as  the  3-foot  lengths 
of  the  larger  pipe  would  require  a  derrick  for  handling. 

There  are  some  advocates  and  users  of  cement  sewer- 
pipe.  The  city  (now  borough)  of  Brooklyn,  N.  Y.,  used 
it  almost  exclusively  for  thirty-five  years  or  more,  but  has 
laid  practically  none  since  1905.  It  has  the  advantage  over 
clay  pipe  that  it  can  be  moulded  to  exactly  the  size  and  shape 
desired,  while  the  clay  shrinks  and  sometimes  warps  in  burn- 
ing. It  is  therefore  possible  to  obtain  a  sewer  with  a  more 
uniform  bore  by  using  cement  pipe;  also  to  obtain  the  advan- 
tage (not  very  considerable  under  most  circumstances)  of  a 
flat  base,  as  shown  in  Plate  VI,  Fig.  I. 

When  this  pipe  is  made  of  good  cement  and  sand  and  this 
is  properly  proportioned  and  mixed  it  should  give  a  material 
which  will  improve  with  age.  It  is,  however,  more  difficult 
to  detect  the  quality  of  a  cement  than  of  a  vitrified  clay  pipe, 
and  much  worthless  cement  pipe  has  consequently  been  put 
upon  the  market.  Clay  pipe  has  a  somewhat  smoother  sur- 
face, but  this  difference  grows  less  with  age,  owing  to  the 
coating  which  forms  on  each. 

Cement  pipe  weighs  from  50  to  100  per  cent  more  than 
clay  pipe  of  the  same  diameter,  and  hence  both  freight  and 
expense  of  handling  are  increased.  Good  cement  piffc  is  in 
most  places  more  expensive  than  good  clay  pipe. 


158  SEWERAGE. 

ART.  42.    MANHOLES,  "LAMP-HOLES,  FLUSH-TANKS,  ETC. 

The  purpose  of  manholes,  as  the  name  implies,  is  to  give 
admittance  to  the  sewers,  which  is  necessary  for  the  purpose 
of  inspection  and  cleaning.  They  should  therefore  be  suffi- 
ciently large  to  permit  a  man  of  average  size  to  enter  and  work 
in  them. 

Manholes  are  in  general  built  immediately  above  a  sewer 
and  leading  from  it  to  the  ground-surface.  In  the  case  of 
some  large  sewers  in  Europe  they  are  built  at  one  side  of  the 
sewer  and  connected  with  it  by  an  underground  passage,  the 
chief  advantages  of  which  construction  are  the  greater  con- 
venience for  entering  and  the  avoiding  of  manhole-heads  in 
the  street-paving.  But  this  construction  is  very  expensive 
and  the  passage  is  liable  to  be  a  collector  of  filth. 

The  size  of  vertical  manholes  is  usually  24  inches,  although 
sometimes  only  22  or  even  20  inches,  diameter  at  the  top, 
increasing  towards  the  bottom  to  a  size  in  which  a  man  can 
work.  The  least  size  advisable  for  the  bottom  on  lines  of 
pipe  sewers  is  4  feet  circular  or  3  feet  by  4  feet  6  inches 
oval.  In  manholes  of  this  size  the  ordinary  operations  of 
inspection  and  cleaning  of  pipe  sewers  can  be  carried  on. 
There  is  no  particular  advantage  in  having  an  ordinary  man- 
hole of  more  than  5  feet  interior  diameter. 

Wherever  possible  the  sides  of  the  manhole  should  be  built 
vertical  from  the  side  benches  of  the  bottom  (ab  and  cd,  Plate 
VIII,  Fig.  5)  to  a  point  3  feet  above,  from  which  point  they 
may  be  brought  in  with  a  straight  batter  to  the  smaller  top, 
which  is  usually  circular.  Where  the  depth  of  the  top  of  the 
sewer  below  the  surface  is  less  than  7  feet  this  construction 
becomes  difficult,  owing  to  the  considerable  angle  which  the 
upper  walls  must  make  with  the  vertical.  The  slope  cannot 
well  begin  at  a  lower  point  than  that  stated  and  leave  work- 


DETAIL    PLANS. 


FIG.  7.  BROOKLYN,(N.  Y.) 
MANHOLE  COVER.  1896. 


IP  a  a  a  a  a 
Id  a  a  a  a  a 
£  a  a  a  a  a 

I&  a  a  a  a  p 
0  a  a  a  a  a 


FIG.  8. 
MANHOLE  BUCKET. 


FIG.  1  1. 
BRICK  LAMPHOLE. 


FIG.  9    VENTILATING 
MANHOLE  HEAD, 


160  SEWERAGE. 

ing-room  at  the  bottom.  If  the  depth  of  sewer  is  more  than 
$  feet  this  difficulty  can  be  met  by  arching  the  walls  (see 
Plate  IX,  Fig.  2),  which  construction  requires  careful  work- 
manship. An  alternative  method,  especially  adapted  to  a 
depth  of  less  than  5  feet,  is  to  reduce  the  area  of  the  manhole 
near  the  top  by  an  offset,  using  either  a  brick  arch  or  an  iron 
beam  to  span  the  offset  (see  Plate  IX,  Fig.  3).  If  the  man- 
hole is  more  than  10  feet  deep  the  diameter  should  increase 
more  rapidly  for  the  first  3  feet  down  from  the  top,  being  at 
least  2  feet  9  inches  at  that  depth,  as  otherwise  descent 
through  the  shaft  will  be  difficult. 

Descent  through  the  manhole  can  be  made  by  means  of  a 
ladder  or  a  rope,  but  it  is  customary  to  build  steps  into  the 
wall  for  this  purpose.  These  may  consist  of  protruding 
bricks  or  stones  or  cast-  or  wrought-iron  pieces.  The  first 
offer  but  precarious  footing,  cast  iron  is  not  so  reliable  as 
wrought  and  costs  little,  if  any,  less:  the  last  is  therefore  recom- 
mended. These  steps  are  made  of  various  shapes.  The  sim- 
plest and  probably  as  good  as  any  is  one  made  of  a  round  bar 
bent  and  the  ends  flattened  as  shown  in  Plate  IX,  Fig.  4.  The 
steps  should  be  placed  about  14  inches  (6  bricks)  apart  verti- 
cally, and  either  directly  under  each  other  or  alternating  on  each 
side  of  a  vertical  line,  the  former  in  narrow  shafts. 

Manholes  oval  at  the  bottom  are  well  adapted  to  locations 
where  there  are  no  intersecting  sewers;  those  circular,  to 
points  of  intersection. 

Where  one  sewer  crosses  another  without  intersecting  it  a 
manhole  of  special  construction,  permitting  of  inspecting 
each  sewer,  is  desirable.  Such  a  one  is  shown  in  Plate  IX, 
Fig.  5,  in  which  the  upper  sewer  is  continued  through  the  man- 
hole by  an  iron  trough. 

While  at  the  junction  of  a  pipe-sewer  main  and  lateral  the 
latter  should  be  at  a  somewhat  higher  elevation  than  the 
former,  the  difference  in  elevation  of  the  crowns  of  the  two  should 


DETAIL   PLANS. 


161 


FIG.  8.  DROP  MANHOLE. 


FiG.  9.  FIG.  7.  DEEP-CUT 

MANHOLE  WITH  SUBDRAIN  'HOUSE  CONNECTION. 

INSPECTION  HOLE. 


1 62  SEWERAGE. 

not  exceed  6  inches.  To  obtain  this  result  the  lateral  may, 
if  necessary,  be  lowered  a  sufficient  amount  at  its  end  by  increas- 
ing the  grade  from  the  previous  manhole.  If  this  would  in- 
crease the  depth  of  excavation  by  more  than  3  or  4  feet  a 
drop  between  the  sewers  may  be  made  at  the  manhole.  This 
should  be  so  arranged  that  each  sewer  will  be  accessible  for  clean- 
ing. The  drop  should  not  be  made  through  the  shaft  of  the 
manhole,  but  through  a  small,  smooth  channel.  A  good  design 
is  that  shown  in  Plate  X,  Fig.  8. 

When  sub-drains  are  laid  under  large  sewers  arrangements 
for  cleaning  them  may  be  made  as  shown  in  Plate  VI,  Fig.  6, 
by  a  vertical  branch  opening  into  a  manhole;  or  if  they  are 
under  the  centre  of  the  sewer  such  a  pipe  may  open  into  the 
sewer-invert,  the  opening  being  ordinarily  tightly  closed  by  a 
cap  or  plug.  When  the  sub-drain  is  under  a  small  sewer  the 
branch  pipe  should  lead  into  a  manhole,  opening  either  in  the 
sewer-invert  or,  better,  in  the  bench.  In  either  case  the 
opening  should  be  plugged  so  that  absolutely  no  sewage  can 
enter  it  (see  Plate  X,  Fig.  9). 

Manholes  of  special  design  will  be  required  by  unusual 
conditions,  but  in  all  the  three  principal  requirements  of  a 
manhole  should  be  met:  it  should  offer  easy  access  for  inspec- 
tion and  cleaning  of  the  sewer,  and  ventilation  of  the  same; 
it  should  also  be  so  proportioned  as  to  resist  the  pressure  of 
the  surrounding  earth.  For  this  last  purpose  the  curved  form 
is  better  than  the  polygonal. 

Manholes  for  sewers  larger  than  30  to  36  inches  are  usually 
built  up  from  the  sewer-arch  and  have  no  special  bottom  con- 
struction. The  sewer-invert  under  the  manhole  should  be 
reinforced,  however,  if  the  ground  is  at  all  yielding.  The 
manhole-shaft  is  sometimes  placed  on  one  side  of  the  sewer 
both  for  strength  and  for  facility  of  access  (see  Plate  IX,. 
Fig.  6). 

The  foundation  of  a  manhole  should  be  perfectly  solid. 


DETAIL  PLANS.  163 

If  the  soil  is  soft  a  plank  platform  may  be  used.  Owing  to 
the  irregular  shape  of  the  bottom,  concrete  usually  gives 
better  results  as  to  strength,  shape,  and  imperviousness  than 
does  brick-work.  The  bore  of  each  sewer  should  be  continued 
through  the  bottom  by  a  smooth  channel  of  uniform  section 
and  slope,  either  straight  or  with  a  continuous  curve.  This 
channel  can  be  plastered  with  Portland  cement,  lined  with 
brick  or  with  split  vitrified  pipe.  The  last  method  gives  the 
smoothest  surface  and  is  the  one  most  likely  to  give  a  straight 
channel  of  uniform  size.  For  curved  channels,  if  split  bends 
of  the  desired  radius  cannot  be  had,  brick  plastered  with  Port- 
land cement  is  recommended.  The  channels  should  have 
vertical  sides  carried  up  to  a  point  at  least  $  as  high  above  the 
invert  as  the  top  of  the  sewer-pipe,  and  benches  should  slope 
up  to  the  sides  of  the  manhole  at  an  angle  of  at  least  10°  cr 
15°  with  the  horizontal. 

The  manhole  walls  are  usually  built  of  brick,  8  inches  thick 
from  the  top  to  a  point  10  or  12  feet  below  the  surface,  and 
increasing  in  thickness  with  the  depth.  If  the  bottom  is  a 
circle  or  a  well-designed  oval  with  no  radius  greater  than  6 
feet  a  1 2-inch  wall  should  be  strong  enough  at  any  depth, 
unless  the  ground  is  a  quicksand  or  similar  material  or  is  very 
wet.  The  outside  of  the  manhole  should  be  plastered  with 
cement  mortar  to  keep  out  ground-water  or  water  used  in 
settling  the  trenches,  and  to  prevent  the  lifting  of  the  top 
foot  or  two  by  freezing  ground. 

In  several  cities  manholes  have  been  built  entirely  of  con- 
crete. These  are  generally  more  water-tight  than  brick  ones, 
and  stronger.  Special  forms  are  required  for  their  construction. 

The  top  of  the  manhole  is  generally  capped  with  an  iron 
casting  sufficiently  deep  to  permit  the  laying  close  to  it  of  brick 
or  stone  paving.  This  will  be  about  8  or  10  inches,  except 
where  the  paving  is  made  for  heavy  or  city  traffic,  where  it  may 
need  to  be  12  to  16  inches. 


1 64  SEWERAGE. 

Where  the  street  is  not  paved,  each  manhole-head  should 
be  surrounded  for  a  distance  of  at  least  2  feet  by  cobble, 
rubble  or  stone  block  paving,  to  protect  both  it  and  passing 
vehicles. 

The  cover  should  be  sufficiently  strong  to  support  the  heaviest 
wheel-pressure.  It  should  be  provided  with  ventilation-holes 
giving  as  much  area  of  opening  as  possible.  Its  upper  surface 
should  be  roughened  to  provide  foothold  for  horses.  It  should 
offer  as  little  obstruction  as  possible  to  traffic,  and  be  practi- 
cally noiseless.  The  ventilation-holes  should  be  through  the 
elevated  rather  than  through  the  depressed  parts  of  the  cover, 
since  by  this  construction  the  stoppage  of  the  holes  by  dirt  and 
snow  and  the  entrance  of  dirt  into  the  sewer  are  considerably 
lessened.  Such  a  manhole-head  and  -cover,  as  used  in 
Brooklyn,  N.  Y.,  is  shown  in  Plate  IX,  Fig.  7.  Covers 
are  sometimes  provided  with  locks  to  prevent  the  opening  of 
the  manhole  by  unauthorized  persons,  but  much  trouble  is  in 
some  instances  caused  by  these  locks,  particularly  in  freezing 
weather.  A  better  plan  probably  is  to  make  the  covers  so 
heavy  that  they  cannot  readily  be  raised  without  the  use  of  some 
strong  implement  adapted  to  this  purpose. 

On  roads  and  streets  not  paved  with  hard  permanent  pave- 
ment, more  or  less  dirt  will  be  sure  to  enter  through  the  venti- 
lation-holes and  if  allowed  to  reach  the  bottom  of  the  manhole 
will  tend,  particularly  in  small  sewers,  to  form  stoppages.  To 
prevent  this  a  bucket  of  some  kind  should  be  suspended  under 
the  holes,  smaller  than  the  manhole-opening,  that  the  air  may 
pass  up  between  the  bucket  and  the  walls,  or  a  special  construc- 
tion of  some  kind  should  be  designed  for  this  purpose  (see  Plate 
IX,  Figs.  8  and  9).  These  receptacles  should  be  cleaned  be- 
fore they  become  filled  with  dirt,  for  which  purpose  the  remov- 
able bucket  of  Fig.  8  is  the  more  convenient.  The  bucket 
supports  must  be  so  strong  that  the  bucket  cannot  drop  into 
the  sewer,  even  when  filled  with  dirt  or  ice.  Another  objection 


DETAIL  PLANS.  165 

to  Fig.  9  is  the  larger  amount  of  street-surface  occupied  by  the 
iron  head. 

Lamp-holes  may  be  from  8  to  12  inches  in  diameter  and 
are  placed  vertically  above  the  sewer.  They  are  sometimes 
made  by  placing  in  the  pipe-line  a  T  branch  pointing  upward 
and  resting  a  vertical  line  of  sewer-pipe  in  it.  This  is  decidedly 
poor  construction,  as  the  branch  pipe  is  liable  to  be  crushed 
by  the  weight.  The  upright  pipes  should  be  supported  by  a 
foundation  of  brick  or  concrete  or  the  entire  shaft  should  be  of 
brick.  The  latter  is  much  to  be  preferred,  since  the  pipe  con- 
struction is  almost  sure  to  be  pushed  out  of  line  by  the  settling 
of  the  back-filling. 

The  foundation  of  a  lamp-hole  should  be  firm,  the  invert 
formed  as  shown  in  Plate  IX,  Fig.  n.  The  head  it  would 
be  well  to  provide  with  ventilation-holes,  but  this  is  seldom 
done. 

A  flush-tank  should  be  water  tight.  It  should  be  so  propor- 
tioned as  to  hold  the  required  amount  of  water  without 
increasing  the  head  on  the  sewer  beyond  the  limit  set  (Art. 
21).  The  flush-tank  is  usually  set  at  the  upper  end  of  a  sewer- 
line,  toward  which  much  sewer-air  rises,  and  the  sewer  should 
therefore  be  provided  at  that  point  with  ample  ventilation. 
In  spite  of  this,  many  automatic  flush-tanks  are  so  built  as  to 
afford  the  sewer  absolutely  no  ventilation,  forcing  the  adjacent 
houses  to  unwillingly,  and  usually  unknowingly,  provide  it. 
Since  flushing-siphons  cannot  permit  of  ventilation  through  their 
passages,  a  vent  should  be  furnished  the  sewer  just  below  the 
flush-tank.  It  is  advisable  to  combine  with  this  a  lamp-hole, 
as  in  Plate  X,  Fig.  i.  A  still  better  plan  is  to  place  a  ventilat- 
ing-manhole  just  below,  even  in  contact  with,  the  flush-tank. 
However,  if  the  sewer  be  ventilated  through  house  connections 
much  of  this  difficulty  disappears. 

Flush-tanks  are  usually  built  of  brick  with  concrete  bottoms, 
the  whole  being  made  water-tight.  Concrete  would  probably 


166  SEWERAGE. 

be  preferable  in  most  cases,  reinforced  with  steel  rods,  as  this 
would  be  tighter  and  stronger  than  brick. 

The  automatic  flushing  appliances  in  common  use  act  on 
the  principle  of  the  siphon,  the  variations  being  in  the  method  of 
starting  the  flow.  Most  of  those  now  used  have  no  moving 
parts  whatever,  such  as  the  Rhoads-Williams  and  Miller  tanks. 
A  number  of  other  ideas  have  been  used  for  flush-tanks, 
such  as  a  tank  on  trunnions,  which  tips  when  full  and  re- 
turns to  its  original  position  when  empty;  a  collapsing  tube 
which,  as  the  water  rises  in  the  tank,  is  extended  upward  by 
an  attached  float  until  it  reaches  its  full  length,  when  the 
water,  still  rising,  overflows  into  and  through  it  to  the  sewer, 
the  tube  meantime  collapsing. 

The  outlet  of  the  flush-tank  should  be  at  some  elevation, 
the  more  the  better,  above  the  sewer.  If  no  automatic  appli- 
ance is  used  the  opening  of  the  flush-tank  may  be  in  the 
bottom,  stopped  by  a  plug  or  cap,  which  is  raised  by  an 
attached  chain  when  the  tank  is  full;  or  it  may  be  in  the  side 
and  be  opened  and  closed  by  a  valve,  either  sliding  or  hinged. 

If  water  is  led  to  the  flush-tank  by  a  pipe  this  should  be  kept 
below  the  effect  of  frost,  turning  and  rising  to  a  higher  level  inside 
the  flush-tank  if  necessary. 

Inlets  are  made  with  and  without  catch-basins  (see  Art.  36), 
and  the  openings  are  sometimes  vertical,  sometimes  horizontal, 
and  sometimes  inclined.  Their  purpose  being  to  admit  water 
from  the  roadway  to  the  sewer,  the  opening  of  each  inlet  should 
be  sufficiently  large  to  admit  all  the  water  which  can  reach  it 
from  the  heaviest  rain  whose  run-off  the  sewer  is  designed  to 
carry.  It  may  be  so  designed  that  a  smaller  opening  leading 
to  a  house-sewer  shall  pass  the  water  from  small  rains  or  the 
first  washings  of  a  rain,  while  another  larger  one  leads  to  a  storm- 
sewer.  The  opening  should  be  at  the  gutter  where  the  water 
flows,  and  which  may  be  slightly  depressed  at  this  point.  If 
horizontal  in  the  bottom  of  the  gutter  one  large  opening  is  not 


DETAIL  PLANS.  167 

permissible,  but  smaller  ones,  into  which  neither  carriage-wheels 
nor  feet  of  horses  or  pedestrians  can  enter,  must  be  used. 
The  plate  through  which  these  holes  are  made  must  be 
able  to  support  the  most  heavily  loaded  wheels  which  are 
likely  to  come  upon  it. 

If  the  openings  are  through  the  face  of  the  curb,  in  a  plane 
either  vertical  or  slightly  inclined,  they  may  be  much  larger. 
In  some  cases  one  large  opening  is  used,  entirely  unprotected, 
through  which  children  could  and  sometimes  do  fall.  Except 
for  this  danger  such  a  clear  waterway  is  an  excellent  arrange- 
ment. But  it  is  advisable  to  so  place  one  or  more  bars  across 
the  opening  as  to  remove  the  danger  referred  to. 

The  total  area  of  opening  required  may  be  found  approxi- 
mately by  the  hydraulic  formulas  for  flow  through  horizontal 
or  vertical  orifices  or  over  weirs,  as  the  case  may  be.  In  the 
case  of  openings  less  than  2  inches  across  in  any  direction  an 
additional  allowance  should  be  made  for  the  occasional 
stoppage  of  some  of  them  by  leaves,  paper,  etc.  The  vertical 
openings,  being  larger,  are  less  liable  to  stoppage.  If  hori- 
zontal openings  in  the  gutter  are  in  the  shape  of  slots  they  should 
run  across  the  line  of  the  gutter.  Large  gutter  inlets  are  prefer- 
able where  the  water  approaches  with  considerable  velocity. 
Otherwise  the  author  prefers  curb  inlets. 

Between  the  openings  and  the  sewer  the  channel  should 
be  straight  or  have  as  easy  bends  as  possible,  that  the  run-off 
may  have  an  uninterrupted  flow.  The  use  of  a  catch-basin 
greatly  interferes  with  this,  the  water  seething  and  whirling 
in  it  during  storms;  consequently  the  channel  connecting  it 
with  the  sewer  should  be  larger  than  if  a  simple  inlet  were 
used.  In  some  instances  a  pipe  leads  directly  from  the  open- 
ing to  the  sewer,  either  with  or  without  a  water-seal  trap.  It 
is  better,  however,  to  obtain  a  more  substantial  structure  by 
setting  under  the  opening  a  small  basin  with  a  curved  bottom 
from  which  the  pipe  leads  directly  to  the  sewer.  Where  the 


1 68  SEWERAGE. 

opening  is  horizontal  the  basin  is  desirable  to  support  the 
weight  which  may  come  upon  the  grating  and,  where  a  trap 
is  used,  to  enable  it  to  be  placed  below  danger  of  freezing. 
It  also  facilitates  inspection  and  cleaning  of  the  connection- 
pipe  (see  Plate  X,  Fig.  2).  Figs.  3  and  4  show  two  designs 
for  inlet-gratings,  the  latter  particularly  adapted  to  admitting 
large  quantities  of  water. 

A  catch-basin  usually  consists  of  a  well  under  the  inlet- 
opening  and  below  the  connection-pipe  to  catch  the  heavier 
matters.  It  is  sometimes  placed  between  the  inlet  and  the 
sewer  on  the  line  of  the  connection-pipe,  and  sometimes  at 
the  sewer  in  connection  with  a  manhole.  To  be  at  all 
efficient  it  should  extend  more  than  18  inches  below  the  con- 
nection-pipe, since  a  heavy  rain  will  keep  the  water  in  it  so 
stirred  up  as  to  wash  out  any  deposits  above  that  point. 
The  bottom  of  the  catch-basin  should  be  covered  with  a  flag- 
stone or  the  most  substantial  of  concrete-  or  brick-work. 

Inlet  and  catch-basin  wells  may  be  built  of  concrete  or  of 
stone,  but  are  usually  of  brick.  Catch-basin  wells  should  be 
water-tight,  that  water  may  constantly  cover  the  contents  and 
lessen  their  odors.  The  gratings  of  catch-basins  should  be 
removable  or  the  basins  should  be  provided  with  manhole- 
openings  and  the  wells  be  sufficiently  large  to  be  entered  for 
the  inspection  and  cleaning  of  the  connection-pipes. 

When  the  inlet-opening  is  in  the  curb,  the  well  with  its  catch 
basin  (if  one  is  provided)  is  placed  under  the  curb  or  side- 
walk, and  access  to  it  is  through  a  manhole -opening  in  the  side- 
walk. There  is  a  great  variety  of  inlet-tops  for  such  construc- 
tion, both  cast  iron  and  stone  being  used.  The  latter,  where 
not  too  expensive,  is  usually  preferable,  being  neater,  more  dur- 
able, and  usually  more  like  the  contiguous  sidewalk  material 
than  cast  iron.  A  stone-topped  inlet  is  shown  in  Plate  X,  Fig. 
5,  an  iron-topped  one  in  Fig.  6.  In  some  cities  reinforced 
concrete  is  used  instead  of  stone. 


DETAIL  PLANS.  169 

Traps  are  frequently  placed  in  catch-basins  or  the  con- 
necting-pipes to  prevent  the  exit  of  sewer-air,  unwisely,  the 
author  thinks  (see  Art.  36).  The  outside  trap  is  usually  a 
running  or  P  pipe  trap.  Many  varieties  of  inside  trap  have 
been  designed,  both  fixed  and  movable.  The  former  should 
not  prevent  access  to  the  connection-pipe  and  hence  should 
be  at  least  15  inches  from  its  opening.  Traps  with  movable 
parts  should  be  as  simple  as  possible  in  construction  and 
any  trap  should  compel  the  outflowing  water  to  make  the  least 
possible  number  of  angular  changes  of  direction. 

Instead  of  placing  a  catch-basin  at  each  inlet  it  is  some- 
times preferable  to  place  silt-basins  along  the  line  of  the  sewer 
at  intervals  of  1000  feet  or  more,  with  a  manhole  over  each 
for  ventilation  and  cleaning.  These  are  particularly  applica- 
ble to  flat  grades  of  storm  sewers  in  the  separate  system. 
They  consist  of  an  enlargement  of  the  sewer,  and  a  depression 
of  a  foot  or  more  in  its  invert,  into  which  the  heavier  silt  is 
washed,  and  from  which  it  can  be  removed  more  easily  than 
when  deposited  along  a  stretch  of  sewer.  These,  however, 
should  not  be  used  to  encourage  deposit,  but  only  when 
deposits  would  occur  along  the  sewer  if  they  were  not  pro- 
vided. Their  advantage  over  inlet  catch-basins  is  that  the 
odors  reach  the  outer  air  further  from  pedestrians,  and  that 
the  difficulty  and  cost  of  cleaning  is  not  so  great.  They 
should  be  used  in  sewers  which  carry  house-sewage  in  excep- 
tional cases  only.  Inlet  catch- basins  are  generally  preferable 
on  lines  of  combined  sewers  where  much  heavy  dirt  reaches 
the  inlet,  or  on  storm-sewers  where  such  dirt  is  washed  in  in 
very  large  quantities.  ^ 


170  SEWERAGE. 


ART.   43.     INTERCEPTORS  AND  OVERFLOWS. 

The  best  form  of  interceptor  to  be  employed  is  determined 
largely  by  the  character  of  the  system  at  the  point  of  inter- 
ception. If  the  house-sewage  is  to  be  intercepted  from  tribu- 
tary sewers  which  originally  discharged  into  a  near  body  of 
water,  the  interceptor  shown  in  Plate  XI,  Fig.  I,  may  be 
used.  This  "  leaping  weir,"  it  is  believed,  was  first  used  by 
Baldwin  Latham  about  1876.  The  exact  length  of  opening 
required  in  the  invert  can  be  only  approximately  determined. 
It  may  be  made  smaller  than  is  thought  necessary  and  cut  to 
the  right  size,  which  is  ascertained  by  trial,  after  the  sewer  is 
in  use.  It  will  also  probably  be  desirable  to  increase  the 
length  from  time  to  time  as  the  amount  of  house-sewage 
increases.  The  principal  objection  to  this  form  of  interceptor 
is  that,  although  the  storm-water  may  leap  the  opening,  much 
of  the  sand  and  other  heavy  matter  carried  along  the  invert 
of  the  combined  sewer  will  fall  into  the  small  intercepting 
sewer  and  may  be  deposited  there. 

An  interceptor  which  meets  this  objection,  but  which  may 
more  properly  be  called  a  divertor,  is  shown  in  Plate  XI, 
Fig.  2.*  The  flap-valve  shown  is  closed  by  the  rising  of  the 
float,  which  occurs  when  the  amount  of  sewage  becomes 
greater  than  it  is  desired  that  the  house-sewer  carry.  The 
joints  of  the  mechanism  should  be  of  bronze.  A  sewer  does 
not  offer  the  best  conditions  for  the  continued  proper  working 
of  any  mechanism  therein,  but  one  so  simple  as  this  should  give 
little  trouble  in  its  maintenance.  Several  other  designs  of  auto- 
matic mechanism  for  accomplishing-  this  purpose  have  been 
employed. 

*  See  Engineering  Record,  vol.  xxxn,  p.  41. 


DETAIL  PLANS. 


171 


Elate  XI. 


FIG.  1.  INTERCEPTOR  (LEAPING  WEIR), 


FIG.  2.  INTERCEPTOR  (DIVERTING) 


FIG.  3.  STORM  OVERFLOW,  DENVER,  COLO 


FIG.  7. 
SUB-DRAIN, 


FIG.  1O. 

FIG.  9.  DEEP-CUT  HOUSE  HOUSE  CONNECTION 

FIG.  8.  CONNECTION  IN  ROCK.  INSPECTION  HOLE. 

SUB-DRAIN^, 


172  SEWERAGE. 

When  a  sewer,  because  of  improper  designing  or  of 
changed  conditions,  becomes  too  small  to  carry  all  the  sewage 
coming  to  it,  the  excess  above  its  capacity  may  be  diverted 
to  and  carried  by  a  relief-sewer  or  -sewers.  A  relief-sewer 
may  cross  under  and  receive  the  excess  from  several  gorged 
sewers,  or  a  single  sewer  may  overflow  into  several  relief- 
sewers  placed  at  intervals  along  its  length  and  leading  to 
near-by  outlets. 

An  outlet  sewer-main  to  combined  sewers  is  sometimes 
provided  with  overflow  outlets  at  several  points  to  avoid 
increasing  the  size  of  the  main  beyond  the  smallest  necessary 
dimension,  which  is  usually  that  which  will  carry  sufficient 
storm-water  to  afford  such  dilution  to  the  house-sewage  as 
will  render  it  unobjectionable  to  discharge  this  into  an 
adjacent  stream.  The  diversion  into  such  a  relief-sewer  or 
relief  outlet  is  ordinarily  made  by  means  of  an  overflow,  con- 
structed as  shown  in  Plate  XI,  Fig.  3,  or  as  in  Fig.  4,  where 
the  relief-sewer  was  constructed  after  the  smaller  sewers  had 
long  been  in  use. 

ART.  49.    INVERTED  SIPHONS;  SUB-DRAINS;  FOUNDATIONS. 

Inverted  siphons  are  usually  circular  in  section,  since 
always  flowing  full;  usually  of  metal,  since  always  under 
pressure,  although  the  metal  may  be  lined  with  brick  or  other 
material.  The  size  required  has  already  been  referred  to. 
When  laid  under  water  they  should  be  so  weighted  or  covered 
with  earth  or  stone  as  to  prevent  their  floating  when  pumped 
empty  for  inspection  or  cleaning,  and  should  be  absolutely 
tight.  The  inverted  siphon  is  made  sometimes  to  slope  from 
both  ends  to  a  point  near  mid-length,  sometimes  with  a 
vertical  drop  at  one  end,  sometimes  at  both  ends.  The  first 
should  be  adopted  only  when  the  siphon  is  sufficiently  large 


DETAIL  PLANS.  I?3 

to  permit  the  entrance  of  a  man.  When  not  of  such  a  size  it 
should  be  straight  from  end  to  end.  This  will  usually  require 
a  shaft  at  one,  sometimes  at  each,  end,  which  may  also  serve 
as  a  manhole.  It  is  in  most  cases  advisable  to  place  a  catch- 
basin  at  the  foot  of  such  a  shaft,  although  in  place  of  this  a 
basin  in  the  bottom  of  an  enlargement  of  the  sewer  just  above 
the  siphon  is  sometimes  employed.  A  siphon  with  catch- 
basins  is  shown  in  Plate  XI,  Fig.  5,  the  valves  on  the  ends  of 
each  siphon-pipe  permitting  either  siphon  to  be  closed  to 
sewage  and  pumped  out  for  inspection,  while  the  other  is  in 
use. 

Unless  a  siphon  under  water  is  of  large  size  and  in  tunnel 
or  laid  in  a  trench  in  a  rocky  bottom  it  should  be  protected 
from  undermining  by  currents,  or  movement  by  shifting 
bottoms  or  channels.  This  protection  is  usually  afforded  by 
driving  a  row  of  sheet-piling  on  each  side  of  the  pipe,  the 
space  between  these  being  in  most  cases  excavated  and  filled 
with  concrete.  The  softer  the  material  in  the  bottom  and  the 
stronger  the  currents  the  deeper  the  sheeting  should  be 
driven.  If  the  bottom  is  too  hard  to  permit  of  driving  sheet- 
ing, large  stone  rip-rap  may  be  placed  on  both  sides  and  over 
the  siphon. 

A  sewer  must  sometimes  pass  either  under  or  over  an 
obstruction — such  as  a  water-main,  another  sewer,  etc. — by  a 
siphon,  either  inverted  or  erect.  The  latter  requires  greater 
care  in  construction  and  constant  attention  to  maintain  a 
vacuum  at  the  summit,  and  the  former  is  in  the  majority  of 
cases  the  preferable  construction.  Such  a  siphon  is  usually  a 
few  feet  in  length  only  and  under  but  little  head.  A  man- 
hole should  be  placed  over  or  near  it  when  the  sewer  is  24 
inches  or  more  in  diameter,  since  it  will  probably  need  more 
frequent  cleaning  than  the  other  parts  of  the  line.  If  the 
sewer  is  less  than  24  inches  diameter  a  manhole  should  be 


174  SEWERAGE 

placed  at  the  upper  end  of  the  siphon  (which  should  be 
straight  from  end  to  end),  and  at  the  lower  end  also,  although 
a  lamp-hole  may  be  substituted  here  if  the  siphon  is  not  over 
150  feet  long,  and  makes  only  an  angle  and  not  a  vertical  rise 
at  this  point.  For  such  a  case  see  Plate  XI,  Fig.  6. 

Sub-drains  are  placed  either  directly  beneath  the  sewer  or 
at  one  side  of  the  trench.  When  there  are  no  artificial  foun- 
dations under  the  sewer  the  latter  position  is  to  be  preferred, 
but  is  in  some  instances  much  more  difficult  and  expensive, 
particularly  in  quicksand.  The  sub-drain  should  be  sur- 
rounded with  broken  stone  or  clean  gravel,  varying  preferably 
from  the  size  of  a  hickory-nut  to  that  of  a  pea.  There  should 
be  at  least  3  inches  of  this  under  the  drain  and  6  inches  at  its 
sides  and  top.  In  quicksand  or  similar  material  these  dimen- 
sions should  be  increased  50  to  100  per  cent.  This  stone 
should  be  well  compacted  to  prevent  future  settlement.  The 
joints  of  the  drain  should  be  slightly  open  and  a  5-  or  6-inch 
strip  of  cheese-cloth  or  burlap  wrapped  around  the  pipe  at  the 
joint  to  keep  out  the  dirt.  Or,  if  bell-and-spigot  pipe  is 
used,  a  piece  of  jute  may  be  calked  loosely  into  the  joint  for 
this  purpose. 

If  a  sewer  were  laid  directly  over  this  there  would  be 
danger  of  a  settlement  of  the  same  and  of  leakage  resulting. 
For  this  reason  the  sub-drain  should  be  laid  at  one  side  of  the 
trench  when  the  soil  is  firm,  as  in  Plate  XI,  Fig.  7.  In  quick 
or  running  sand  this  is  practically  impossible  unless  the  trench 
is  very  wide  or  unless  close  sheathing  be  driven  on  each  side 
of  the  sub-trench  and  carried  below  its  bottom;  such  sheath- 
ing not  to  be  removed  after  the  sub-drain  is  laid.  It  would 
usually  be  better  and  cheaper  than  this  to  lay  the  sub-drain 
in  the  centre  of  the  trench  (which  must  of  course  be  close' 
sheathed  in  quicksand),  and  on  the  stone  filling,  when  levelled 
off,  to  place  a  continuous  platform  on  which  to  lay  the  sewer. 
Such  construction  is  shown  in  Plate  XI,  Fig.  8.  A  still 


DETAIL  PLANS.  17$ 

better  construction  in  any  but  firm  soils  is  to  lay  a  pipe  sewer 
in  concrete,  as  in  Plate  VII,  Fig.  3.  Where  a  foundation  is 
necessary  for  the  sewer  the  sub-drain  construction  is  easily 
arranged.  See  Plate  VI,  Fig.  6,  and  Plate  VII,  Fig.  10. 

The  sub-drain  should  be  laid  to  grade  as  carefully  as  the 
sewer  itself.  It  is  seldom  that  a  sub-drain  can  be  so  arranged 
that  inspection  can  be  made  of  it,  and  therefore  perfectly 
straight  alignment  is  not  necessary;  but  there  should  be  no 
sharp  angles  in  its  line,  which  might  cause  obstructions  or 
interfere  with  the  future  cleaning  of  it.  If  cellars  and  base- 
ments are  to  be  connected  with  this  drain, Y  branches  should 
be  inserted  to  permit  of  such  connections,  and  should  be 
covered  similarly  to  the  house-sewer  branches. 

When  house  or  combined  sewers  are  placed  with  their  tops 
more  than  4  or  5  feet  lower  than  the  average  cellar  depth  in 
that  locality  it  is  advisable  to  place  a  standing  house-connec- 
tion above  each  branch,  bringing  it  to  within  3  to  5  feet  of 
the  average  depth  of  the  cellar  bottoms,  but  stopping  at  least 
7  or  8  feet  from  the  surface.  This  is  to  avoid  compelling 
each  householder  along  the  line  to  dig  down  to  a  deep  sewer 
branch  in  order  to  make  a  connection.  These  standing  con- 
nections are  built  while  the  sewer-trench  is  open,  and  are 
covered  at  the  top  with  a  cap  or  cover  similar  to  house- 
branches.  They  should  not  merely  rest  in  the  branch,  but  a 
foundation  of  concrete  or  brick  masonry  should  support  each. 
The  vertical  pipes  should  be  held  in  place  during  back-filling, 
as  by  stakes  driven  into  the  bank.  In  the  case  of  a  rock  cut, 
or  where  the  banks  are  not  firm,  the  standing  connection  may 
be  inclosed  by  a  vertical  trough  of  planks,  between  which  and 
the  pipe  earth  is  packed,  this  trough  being  held  firmly  in 
place  until  the  trench  is  filled  and  tamped.  If  the  banks  are 
liable  to  cave,  sheathing  should  be  driven  at  each  such  con- 
nection, and  neither  it  nor  the  braces  removed  when  the 
trench  is  filled.  A  standing  house-connection  in  firm  soil  is 


176  SEWERAGE. 

shown   in    Plate  X,  Fig.  7.     One   in   a   rock  cut  is  shown  in 
Plate  XI,  Fig.  9. 

A  sewer  in  soft  soil,  like  any  other  structure,  requires  a 
foundation.  Since  the  weight  is  not  comparatively  great  the 
service  of  the  foundation  is  more  often  to  distribute  the  pres- 
sure and  prevent  local  settling  or  heaving  than  to  prevent  the 
subsidence  of  the  sewer  as  a  whole.  This  purpose  is  usually 
achieved  by  use  of  a  cradle  (Plate  VI,  Fig.  4)  or  a  platform 
of  plank  (Plate  VI,  Fig.  5),  the  former  in  comparatively  firm 
soils  like  damp  sand  or  loam,  the  latter  in  swamp-muck, 
quicksand,  etc.  Where  muck  or  other  soft,  water-sogged  soil 
is  encountered  it  may  be  necessary  to  drive  piles  and  rest  a 
timber  platform  upon  these.  Such  a  foundation  is  shown  in 
Plate  VI,  Figs.  3  and  6.  Where  a  platform  is  used  it  is 
necessary  to  fill  the  sub-invert  spaces  of  the  sewer  with 
masonry.  All  sewers  in  soft  soils  should  have  their  inverts 
arching  downward  to  resist  the  upward  thrust  of  the  ground 
between  the  side  walls,  since  the  weight  of  the  masonry  is 
largely  concentrated  in  these  wails. 

In  rock  excavations  no  part  of  the  pipe  sewer  should  come 
within  6  inches  of  the  rock  bottom,  and  the  space  between  this 
and  the  sewer  should  be  filled  with  sand  or  other  soil  which  com- 
pacts readily,  which  should  be  thoroughly  tamped  to  prevent 
settlements  of  the  invert;  or  the  pipes  should  be  bedded  in  con- 
crete, in  which  case  the  rock  may  be  taken  out  only  to  the  under 
side  of  the  pipe.  If  the  sewers  are  built  of  masonry  this  should 
be  carried  to  rock  everywhere  under  the  invert. 


CHAPTER    VIII. 
SPECIFICATIONS,  CONTRACT,   ESTIMATE   OF  COST. 

ART.  45.     DEFINITION  AND  CLASSIFICATION  OF  SPECIFICA- 
TIONS. 

PUBLIC  work  is  frequently,  if  not  in  the  majority  of  cases, 
done  by  contract  by  a  "  party  of  the  second  part  "  who  is 
paid  for  this  work  by  the  city,  the  "  party  of  the  first  part." 
That  the  contractor  shall  do  the  work  as  the  city  desires,  it  is 
necessary  that  he  be  instructed  what  is  desired  and  that  he 
bind  himself  to  follow  the  instructions.  This  should  all  be 
recorded  in  writing  for  the  protection  of  both  the  city  and  the 
contractor.  The  agreement  to  perform  the  work  on  the  one 
hand  and  to  pay  for  the  same  on  the  other  is  called  a  contract 
and  is  generally  accompanied  by  a  bond  under  which  the  con- 
tractor places  himself  to  perform  the  work  as  directed. 

The  directions,  called  "specifications,"  "  consist  of  a 
series  of  specific  provisions,  each  one  of  which  defines  and 
fixes  some  one  element  of  the  contract.  These  clauses  relate, 
in  general:  first,  to  the  work  to  be  done;  second,  to  the 
business  relations  of  the  two  parties  to  the  contract." 
(Johnson's  "  Engineering  Contracts  and  Specifications  ") 
The  clauses  in  specifications  for  sewer  construction  referring 
to  the  work  to  be  done  may  be  classified  as  those:  first, 
defining  the  character  of  the  material  to  be  employed ; 
second,  giving  directions,  dimensions,  etc.,  for  excavating 

177 


178  SEWERAGE. 

and  back-filling;  third,  setting  forth  the  methods  to  be 
employed  in  the  construction  of  the  sewer-barrel  and  appur- 
tenances, including  foundations;  fourth,  stating  the  require- 
ments of  the  completed  work,  tests  to  be  made,  etc.  ;  fifth, 
giving  general  directions  for  the  conduct  and  maintenance  of 
the  work,  employment  of  labor,  etc.  Disposal  plants  will 
require  separate  specifications,  varying  with  the  character  of 
the  disposal  employed.  No  general  form  for  such  can  be 
given.  Other  special  features  of  a  system  will  call  for  special 
clauses. 

The  clauses  relating  to  the  business  relations  of  the  two 
parties  to  the  contract  may  be  classified  as  relating  to:  first, 
time  of  commencement  and  of  completion  and  rate  of  prog- 
ress of  the  work;  second,  character  of  labor  and  appliances 
to  be  employed  ;  third,  measurement  of  and  payments  for  the 
work;  fourth,  contractor's  protection  of  and  responsibility 
for  lives  and  property;  fifth,  abandonment,  cancellation, 
assignment  of  contract,  etc.;  sixth,  definition  of  names  and 
terms  employed. 

The  specifications  are  generally  accompanied  by  a  set  of 
plans  which  form  a  part  of  the  specifications  and  contract. 
These  together  should  set  forth  the  work  to  be  done  so  clearly 
as  to  leave  no  point  for  future  dispute.  Care  should  be  taken 
that  contradictory  instructions  are  not  given,  but  that  all 
parts  of  both  plans  and  specifications  mutually  agree.  Too 
great  profuseness  should  be  avoided  as  confusing  to  con- 
tractor, inspector,  and  engineer.  Many  engineers  insert  pro- 
visions which  they  have  no  intention  of  enforcing  under 
ordinary  conditions,  merely  to  be  on  the  safe  side,  or  which 
aim  at  theoretic  perfection  of  details  which  cannot  be  attained 
in  practice  (of  which  fact  their  inexperience  may  make  them 
ignorant).  The  fact  that  some  clauses  in  a  specification 
cannot  be  enforced  is  apt  to  detract  from  the  effectiveness  of 
the  others.  It  is  better  to  make  only  such  requirements  as 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.       179 

experience  shows  are  desirable  and  practicable  and  give  the 
contractor  to  understand  that  these  will  be  rigidly  enforced. 

No  foresight  can  predict  all  the  emergencies  which  may 
arise  in  sewer  construction.  To  provide  for  these  it  must  be 
agreed  that  the  engineer  can  modify  plans  or  methods  of  work 
during  construction,  as  well  as  increase  or  decrease  quanti- 
ties. Work  not  at  first  specifically  provided  for  may  be  made 
the  subject  of  separate  contract,  or  if  but  small  in  quantity 
may  be  done  under  the  original  contract  as  extra  work,  to  be 
paid  for  at  its  cost  plus  such  a  percentage  for  profit  (generally 
10  or  15  per  cent)  as  is  fixed  in  the  contract. 

ART*.  46.     SPECIFICATIONS  FOR  MATERIALS. 

A  set  of  specifications  for  sewer  construction  will  be  given 
and  discussed  in  the  succeeding  pages.  Some  alterations  and 
additions  will  probably  be  required  to  adapt  them  to  any  par- 
ticular case,  but  it  is  thought  that  they  will  be  of  considerable 
service  as  an  illustration  of  both  matter  and  form.  Clauses 
in  brackets  are  given  as  alternatives,  the  one  preferred  by  the 
author  being  placed  first;  the  same  also  holding  true  with 
reference  to  the  lettered  paragraphs. 

Paragraph  I.  a.  Sewer-pipe. — All  pipe  and  specials, 
unless  otherwise  specified,  shall  be  of  the  best  quality, 
salt-glazed,  vitrified  clay  sewer-pipe  of  the  hub-and-spigot 
pattern;  both  body  and  bell  shall  [have  a  thickness  not  less 
than  Y1^  the  inside  diameter  of  the  pipe]  [be  of  standard 
thickness].  Each  hub  shall  be  of  sufficient  diameter  to 
receive,  to  its  full  depth,  the  spigot  end  of  the  next  following 
pipe  or  special  without  any  chipping  whatever  of  either,  and 
also  leave  a  space  of  not  less  than  five-eighths  inch  all-around  for 
the  cement-mortar  joint;  it  shall  also  have  a  depth  from  its 
face  to  the  shoulder  of  the  pipe  on  which  it  is  moulded  .at 
least  if  inches  greater  than  the  thickness  of  said  pipe.  Straight 


i8o  SEWERAGE. 

and  curved  pipe  having  diameters  up  to  and  including  15  inches 
shall  be  furnished  in  3-foot  lengths.  Branches  may  be  in  2-foot 
lengths.  All  pipe  and  specials  shall  be  sound  and  thoroughly 
burned,  with  a  clear  ring,  well  glazed  throughout  and  smooth 
on  the  inside  and  free  from  blisters,  lumps,  or  flakes  which  are 
thicker  than  J  the  nominal  thickness  of  the  pipe  and  whose 
largest  diameters  are  greater  than  -J  the  inner  diameter  of  said 
pipe;  and  pipe  and  specials  having  broken  blisters,  lumps,  and 
flakes  of  any  size  shall  be  rejected  unless  the  pipe  can  be  so 
laid  as  to  bring  all  of  these  defects  in  the  top  half  of  the 
sewer.  No  pipe  having  unbroken  blisters  more  than  J  inch 
high  shall  be  used  unless  these  blisters  can  be  placed  in  the 
top  of  the  sewer.  Pipes  or  specials  having  fire-checks  or 
cracks  of  any  kind  extending  through  the  thickness  shall  be 
rejected.  Any  pipe  or  special  which  betrays  in  any  manner  a 
want  of  thorough  vitrification  or  fusion  or  the  use  of  improper 
or  insufficient  materials  or  methods  in  its  manufacture  shall 
be  rejected. 

No  pipe  shall  be  used  which,  designed  to  be  straight, 
varies  from  a  straight  line  more  than  -J  inch  per  foot  of  length; 
nor  shall  there  be  a  variation  between  any  two  diameters  of  a 
pipe  greater  than  2  per  cent  of  the  nominal  diameter. 

No  pipe  shall  be  used  which  has  a  piece  broken  from  the 
spigot  end  deeper  than  ij  inches  or  longer  at  any  point  than 
\  the  diameter  of  the  pipe;  nor  which  has  a  piece  broken  from 
the  bell  end  if  the  fracture  extends  into  the  body  of  the  pipe, 
or  if  its  greatest  length  is  greater  than  \  the  diameter  of  the 
pipe,  or  if  such  fracture  cannot  be  placed  at  the  top  of  the  sewer. 

(Many  engineers  specify  a  depth  of  bell  only  i  inch  "  greater 
than  the  thickness  of  said  pipe,"  but  it  is  difficult  to  make 
tight  joints  in  actual  practice  with  such  bells.  Frequently  the 
defects  of  sewer-pipe  are  not  referred  to  in  detailt  but  the 
acceptance  or  rejection  made  optional  with  the  engineer  or 
inspector. 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.       181 

If  cement  pipe  is  used  the  following  paragraph  may  be  sub- 
stituted  for  i.  a.) 

Paragraph  i.  b.  Sewer-pipe. — All  pipe  and  specials, 
unless  otherwise  specified,  shall  be  of  the  best  quality  of  cement 
or  concrete  sewer-pipe,  of  the  [hub-and-spigot]  [bevelled- joint] 
pattern ;  it  shall  have  a  thickness  not  less  than  f  inch  plus  ^  the 
diameter  of  the  pipe.  [Each  hub  shall  be  of  sufficient  diameter 
to  receive,  to  its  full  depth,  the  spigot  end  of  the  next  following 
pipe  or  special,  without  any  chipping  whatever  of  either,  and 
also  leave  a  space  of  not  less  than  J  inch  all  around  for  the  cement- 
mortar  joint ;  it  shall  also  have  a  depth  from  its  face  to  the  shoulder 
of  the  pipe  on  which  it  is  moulded  at  least  i  inch  greater  than 
the  thickness  of  said  pipe.]  [The  bevel  on  each  pipe  shall  be 
at  least  25  per  cent  longer  than  the  thickness  of  said  pipe,  with 
an  even  and  firm  edge.] 

All  pipe  shall  be  in  3 -foot  lengths  and  in  section  shall  truly 
correspond  to  their  nominal  shapes.  Each  pipe  shall  have  a  flat 
base  making  exact  right  angles  with  the  vertical  axis  of  the  pipe 
and  with  a  width  equal  to  §  the  interior  horizontal  diameter  of 
said  pipe.  The  inside  surface  of  the  pipe  shall  be  smooth  and 
true,  and  not  pipe  shall  be  patched  with  cement  or  otherwise. 
When  it  is  broken,  the  pipe  shall  appear  homogeneous,  be  en- 
tirely free  from  cracks  or  voids,  and  generally  uniform,  showing 
pieces  of  fractured  stone  firmly  imbedded  in  the  mortar. 

The  concrete  for  such  pipe  making  shall  be  composed  of  a 
i—  i — 2  mixture  or  stronger  proportion,  containing  at  least  one 
part  (by  volume  as  packed  by  the  manufacturer)  of  the  best 
quality  Portland  cement  answering  all  the  requirements  of  the 
Report  of  Committee  of  the  American  Society  of  Civil  Engineers, 
elsewhere  referred  to,  with  one  part  of  clean,  sharp,  graded  sand, 
passing  a  No.  10  sieve,  and  two  parts  of  clean  granite  or  trap 
rock  not  more  than  three-eighths  (f)  of  an  inch  in  greatest  diam- 
eter, uniformly  graded  in  size  and  entirely  free  from  sap,  seamy 
or  soft  stone. 


1 82  SEWERAGE. 

Methods  of  moulding,  trimming,  and  seasoning  pipe  are  left 
to  the  discretion  of  the  manufacturer;  as  furnished  it  shall  be 
without  warps,  cracks  or  imperfections,  and  must  not  be  deliv- 
ered on  the  work  or  used  within  sixty  (60)  days  after  manufacture. 

Paragraph  2.  a.  Drain-pipe.  Pipe  for  sub-drains  shall 
be  of  vitrified  clay  sewer-pipe  in  i-  or  2 -foot  lengths  [of  the 
hub-and -spigot  pattern]  [without  bells  or  sleeves].  It  shall 
comply  with  the  specifications  for  sewer-pipe  in  so  far  as 
these  refer  to  thickness,  quality,  and  vitrification  of  material, 
blisters,  lumps,  flakes,  cracks,  and  breaks;  except  that  the 
engineer  may  at  his  option  accept  pipe  having  small  fire- 
cracks  or  checks. 

Paragraph  2.  b.  Drain-pipe. — Pipe  for  sub-drains  shall  be 
composed  of  the  best  quality  of  drain-tile  of  [circular]  [horse- 
shoe] cross-section  in  [one-]  [two-]  foot  lengths.  They  shall 
be  hard-burned  and  without  cracks  or  any  considerable  de- 
parture from  their  nominal  shape,  size,  or  cross-section. 

Paragraph  3.  Brick. — For  all  brick-work  none  but  the 
best  quality  of  sound,  hard-burned,  perfect-shaped  bricks, 
presenting  a  regular  and  smooth  surface,  shall  be  used.  After 
being  thoroughly  dried  and  immersed  in  water  for  24  hours 
they  shall  not  absorb  more  than  10  per  cent  by  weight  of 
water.  Shale  brick,  if  used,  shall  be  composed  of  rock 
thoroughly  ground  and  shall  be  homogeneous  throughout  and 
uniformly  burned. 

Paragraph  4.  Paving-stone. — This  shall  consist  of  hard 
granite  or  trap-rock,  uniform  in  grain  and  texture.  The 
blocks  must  be  rectangular  in  form,  not  less  than  3  nor  more 
than  4  inches  in  breadth,  nor  less  than  4  nor  more  than  5  inches 
in  depth,  and  so  split  and  dressed  with  true  surfaces  that  on 
neither  top,  ends,  nor  sides  shall  there  be  a  projection  from  the 
general  surface  exceeding  J  inch. 

(This  stone  is  used  for  inverts  where  there  is  excessive  ve- 
locity in  the  sewer  or  impact  from  falling  water.) 


SPECIFICATIONS,  CONTRACT,  ESTIMATE    OF   COST.       183 

Paragraph  5.  Masonry-stone. — Stone  for  foundations 
and  backing  shall  be  of  a  sound  and  durable  quality,  free  from 
cracks  and  seams,  having  top  and  bottom  beds  approximately 
parallel.  No  stone  shall  be  less  than  4  inches  thick,  12 
inches  long,  and  8  inches  wide. 

Paragraph  6.  Iron  Castings. — All  iron  castings  shall  be 
made  from  a  superior  quality  of  gray  iron,  remelted  in  the 
cupola  or  air-furnace,  tough  and  of  even  grain,  and  shall 
possess  a  tensile  strength  of  not  less  than  18,000  pounds  per 
square  inch.  Test-bars  of  the  metal  3  inches  by  £  inch,  when 
placed  upon  supports  18  inches  apart  and  loaded  in  the 
centre,  shall  have  a  transverse  breaking  load  of  not  less  than 
looo  pounds,  and  shall  have  a  total  deflection  of  not  less  than 
f  inch  before  breaking.  These  test-bars  shall  be  poured  from 
the  ladle  at  any  time  the  engineer  directs,  before  or  after  the 
castings  have  been  or  while  they  are  being  poured.  All 
castings  shall  conform  to  the  shape  and  dimensions  shown 
upon  the  drawings  and  shall  be  clean  and  perfect,  without 
blow-  or  sand-holes  or  defects  of  any  kind.  No  plugging  or 
other  stopping  of  holes  will  be  allowed.  The  castings  shall 
be  thoroughly  cleaned  of  all  lumps  and  subjected  to  careful 
hammer  tests,  after  which  they  are  to  be  dipped  in  a  bath  of 
coal-tar  pitch  heated  to  at  least  200°  Fahr. 

Iron  pipe  shall  comply  with  the  above  specifications, 
except  that  the  engineer  may,  at  his  option,  receive  a  pipe 
having  a  limited  number  of  small  sand-  or  blow-holes  on  its 
exterior  surface.  No  portion  of  the  shell  of  the  pipe  shall 

have  a  less  thickness  than (this  thickness  can  generally  be 

made  the  least  which  will  permit  of  handling  of  the  pipe  with- 
out danger  of  breaking  it,  and  non-uniformity  of  shell  is  not 
objectionable  if  payment  is  not  made  by  weight). 

Paragraph  7.  Wrought  Iron. — All  wrought  iron  must  be 
tough,  ductile,  and  fibrous,  of  a  uniform  quality,  free  from 
crystalline  structure,  cinders,  flaws,  or  cracks.  In  bars  it 


1 84  SEWERAGE. 

must  have  an  ultimate  strength  of  50,000  pounds  per  square 
inch.  Iron  which  has  been  burnt  in  the  forge  will  be  rejected. 
Each  wrought-iron  piece  furnished  shall  correspond  in  all  respects 
to  the  dimensions  specified. 

Paragraph  8.  Sand.—  All  sand  shall  be  of  the  best  qual- 
ity locally  available,  clean,  sharp,  and  free  from  loam  or  vege- 
table matter,  nor  contain  more  than  5  per  cent  of  clay  or  other 
very  fine  material.  All  particles  must  be  sufficiently  small  to 
pass  a  screen  having  4  meshes  per  lineal  inch. 

(Dirt  in  sand  can  usually  be  detected  by  rubbing  a  small 
amount  on  the  palm,  which  will  be  soiled  by  any  clay  or  loam 
present.) 

Paragraph  9.  Cement. — Unless  otherwise  specified  all 
cement  shall  be  of  the  best  quality  of  Portland  cement  and  tests 
will  be  made  in  general  in  accordance  with  the  present  standard 
methods  of  the  American  Society  for  Testing  Materials,  with 
limits  as  follows: 

Specific  gravity  not  less  than  3.1. 

Fineness,  92  per  cent,  passing  100  sieve,  75  per  cent,  passing 
200  sieve. 

Time  of  setting — initial,  not  less  than  30  minutes;  hard, 
between  one  and  ten  hours. 

Tensile  strength,  pounds  per  square  inch: 

Age.  Neat.  i  Cement,  3  Sand.   . 

24  hours  175 

7  days  500  150 

28  days  600  200 

SOUNDNESS. — Pats  satisfactory  for  28  days  in  air,  and 
also  one  day  in  air  and  27  days  in  cool  water;  also  in  steam 
for  five  hours  after  hard  set.  Anhydrous  sulphuric  acid 
(SO3)  less  than  1.75  per  cent;  magnesia  (MgO)  less  than  4  per 
cent. 


SPECIFICATIONS,    CONTRACT,   ESTIMATE  OF  COST.        185 

A  sufficient  stock  of  cement  shall  be  kept  near  the  site  of 
the  work  in  a  weather-tight  and  moisture-proof  building.  At 
least  ii  days  shall  be  afforded  for  testing.  Cement  may  be 
tested  as  often  as  necessary,  and  if  found  unsatisfactory  will 
be  rejected,  and  must  be  removed  from  the  work. 

The  engineer  shall  be  allowed  to  test  all  cement  and  notice 
of  its  receipt  by  the  contractor  must  be  made  to  the  engineer 
at  least  48  hours  in  advance  of  its  use  upon  the  work.  Any 
cement  not  satisfactory  to  him  shall  be  at  once  removed  from 
the  work. 

Paragraph  10.  Gravel  or  Broken  Stone. — Gravel  or 
broken  stone  as  required  for  foundations  in  the  trench,  or  for 
concrete,  shall  be  clean  material,  of  a  hard,  durable  and  accept- 
able character.  When  used  for  concrete  and  when  so  ordered, 
it  shall  be  carefully  screened  to  a  size  that  will  pass  a  ij-inch 
ring  and  be  retained  on  a  |-inch  ring,  with  the  particles  well 
graded  in  size  between  these  limits. 

Paragraph  u.  Packing. — Packing  may  consist  of  flax, 
jute,  oakum,  or  hemp,  clean  and  with  long  fibres  looselv  twisted 
into  strands. 

Paragraph  12.  Timber. — All  timber  and  planking  used 
in  cradles,  platforms,  and  foundations  shall  be  of  spruce,  or 
timber  equally  as  good,  straight,  sound,  free  from  sap,  shakes, 
large,  loose,  or  decayed  knots,  worm-holes,  or  other  imper- 
fections which  may  impair  its  strength  or  durability.  Piles 
shall  be  of  sound,  straight,  live  spruce  or  yellow-pine  timber,  of 
lengths  specified  by  the  engineer  for  each  locality.  They  shall 
be  not  less  than  6  inches  in  diameter  at  the  smaller  end.  The 
bark  shall  be  removed  in  all  cases. 


1 86  SEWERAGE 


ART.  47.     EXCAVATION. 

Paragraph  13.  Classification  of  Materials. — All  ma- 
terials excavated  shall  be  classified  as  either  earth  or  rock. 
No  material  shall  be  classified  as  rock  which  cannot  be 
removed  more  cheaply  by  drilling  and  blasting  than  by  pick- 
ing, except  that  any  boulder  measuring  ^  cubic  yard  or  more 
shall  be  so  classified,  whether  blasted  or  removed  bodily;  but 
such  boulder  shall  not  be  returned  to  the  trench  without  being 
first  broken  up. 

Paragraph  14.  Excavation  of  Trench. — The  trench  shall 
be  excavated  along  the  line  designated  by  the  engineer  and 
to  the  depth  necessary  for  laying  the  sewer  or  sub-drain  at  the 
grade  given  by  him.  In  the  case  of  pipe  sewers  it  shall  be  I  foot 
wider  at  the  bottom  than  the  outside  diameter  of  the  pipe, 
and  for  brick  sewers  as  wide  as  the  greatest  external  horizon- 
tal width  of  the  structure  to  be  placed  therein,  without  any 
undercutting  of  the  banks.  Where,  in  the  opinion  of  the 
engineer,  the  original  earth  is  sufficiently  compact  and  solid 
for  the  foundation  of  the  work  the  contractor  shall  excavate 
the  bottom  of  the  trench  to  conform  to  the  external  form  and 
dimensions  of  the  invert  or  foundation  as  ordered.  For  pipe 
sewers  the  bottom  of  the  trench  under  each  bell  shall  be  so 
hollowed  out  as  to  allow  the  body  of  the  pipe  to  have  a  bear- 
ing throughout  on  the  trench  bottom  and  permit  of  making 
the  joint.  In  case  a  trench  be  excavated  at  any  place, 
excepting  at  joints,  below  the  proper  grade  it  shall  be  refilled 
to  grade  with  sand  or  other  readily  compacted  material,  thor- 
oughly rammed,  without  extra  compensation  unless  the  extra 
excavation  was  ordered  by  the  engineer. 

The  material  excavated  shall  be  laid  compactly  on  the  side 
of  the  trench  and  kept  trimmed  up  so  as  not  to  endanger  the 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.       187 

work  and  to  be  of  as  little  inconvenience  as  possible  to  the 
travelling  public  and  to  adjoining  tenants.  Where  required, 
excavated  material  shall  be  confined  within  narrow  limits  by 
suitable  wooden  fences  or  retainers.  All  trees  in  the  vicinity  of 
the  work  shall  be  protected.  Where  the  street  is  paved  the 
paving  shall  be  kept  separate  from  the  other  material  excavated. 
{//  is  generally  desirable  to  place  the  paving  material  on  the  side 
of  the  trench  which  is  to  be  left  open  for  travel,  and  the  earth  upon 
the  other.)  All  streets  shall  be  kept  open  for  travel  and  the 
engineer  reserves  the  right  to  require  the  use  of  excavating- 
machinery  if  necessary  to  insure  this. 

No  tunnelling  will  be  allowed  except  by  written  permit,  with 
restrictions,  from  the  engineer.  When  tunnelling,  the  contractor 
will  excavate  the  material  to  such  cross-section  as  may  be  desig- 
nated, using  timbering  or  other  tunnel-lining  and  shoring  satis- 
factory to  the  engineer.  The  location  and  size  of  any  shafts, 
and  the  location  of  pumps,  derricks,  boilers,  and  other  machinery, 
must  be  approved  by  the  engineer  (see  Art.  64).  The  engineer 
shall  have  the  right  to  limit  the  amount  of  trench  which  shall 
be  opened  or  partly  opened  or  street  surface  which  shall  be 
disturbed  at  any  one  time  in  advance  of  the  completed  sewer, 
and  also  the  amount  of  trench  left  unfilled  and  unrestored. 

The  contractor  shall  not,  without  permission  from  the  engineer 
remove  from  the  line  of  work  any  sand,  gravel,  or  earth  excavated 
therefrom  which  may  be  suitable  for  refilling  the  trench  until 
the  same  shall  have  been  refilled. 

Paragraph  15.  Pumping  and  Bailing. — The  contractor 
shall  furnish  all  necessary  machinery  for  the  work,  shall  pump, 
tail,  or  otherwise  remove  any  water  which  may  be  found  or 
shall  accumulate  in  the  trenches,  and  shall  perform  all  work 
necessary  to  keep  them  clear  of  water  while  the  foundations  and 
the  masonry  are  being  constructed  or  the  sewer  laid.  No  struc- 
tures or  pipe  sewers  shall  be  laid  in  water.  In  no  case,  unless 
by  special  permission  of  the  engineer,  shall  water  be  allowed 


1 88  SEWERAGE. 

to  rise  onto  or  run  over  the  invert  or  foundation  or  through  the 
sewer  until  the  cement  is  satisfactorily  hardened.  The  disposal 
of  the  water  after  removal  shall  be  satisfactory  to  the  engineer. 

Paragraph  26.  Shoring  and  Sheathing. — The  contractor 
shall  furnish,  put  in  place  and  maintain  such  sheathing  and 
bracing  as  may  be  required  to  support  thoroughly  the  sides 
of  the  excavation  (whether  above  or  below  sewer  grades) 
and  to  prevent  any  movement  which  might  injure  the  sewers, 
delay  the  work  or  interfere  seriously  with  adjoining  struc- 
tures or  operations.  Such  sheathing  and  bracing  shall  be  left 
in  until  the  trench  is  refilled,  all  such  bracing  and  sheathing 
being  done  at  the  contractor's  expense.  Sheathing  left  in 
permanently  by  the  order  of  the  engineer,  and  only  such,  will 
be  paid  for  at  the  price  bid.  When  left  in  the  trench  sheath- 
ing shall  be  cut  off  at  a  point  about  I  foot  below  the  surface. 
The  contractor  shall,  at  his  own  expense,  shore  up  and  other- 
wise protect  any  building  which  may,  in  the  opinion  of  the 
engineer,  be  endangered  by  the  work. 

Paragraph  17.  Railway-crossings. — When  any  railway- 
lines  are  to  be  crossed  or  interfered  with  specific  directions 
as  to  the  time  and  manner  of  doing  this  work  will  be  given  by 
the  engineer,  and  the  contractor  shall  conform  to  such  direc- 
tions. He  shall  be  allowed  for  material  furnished  and  made 
part  of  the  permanent  construction,  so  far  as  it  may  be  addi- 
tional to  that  indicated  on  the  plan,  but  all  other  work  shall 
be  done  at  his  own  cost. 

Paragraph  18.  Interference  with  Existing  Structures 
and  Watercourses. — In  excavating  and  back-filling  trenches 
and  laying  the  sewer  care  must  be  taken  not  to  move  or  injure 
any  gas-,  water-,  sewer-,  or  other  pipes,  conduits,  poles  or  struc- 
tures without  the  order  of  the  engineer.  If  necessary  the  con- 
tractor shall,  at  his  own  expense,  sling,  shore  up,  and  secure, 
and  maintain  a  continuous  flow  in  said  structures,  and  shall 
repair  any  damage  done  to  them  and  keep  them  in  repair  until 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.        189 

the  final  acceptance  of  the  completed  works,  leaving  them  in  as 
good  condition  as  when  uncovered.  Should  it  be  necessary 
to  move  the  position  of  a  pipe  or  conduit  this  shall  be  done 
in  accordance  with  the  instructions  of  the  engineer,  and  the 
contractor  shall  be  allowed  for  material  furnished  and  made 
part  of  the  permanent  construction,  so  far  as  it  may  be  addi- 
tional to  that  indicated  upon  the  plans,  and  for  labor  performed 
on  such  additional  construction,  but  all  other  work  shall  be  done 
at  his  own  expense. 

In  case  of  a  gas,  water  or  other  pipe  becoming  broken  in  the 
prosecution  of  the  work,  the  contractor  shall  give  immediate 
notice  to  the  proper  authorities,  and  shall  be  responsible  for  any 
damage  to  persons  or  property  caused  by  such  breaks,  and  failure 
to  give  prompt  notice  to  the  authorities  shall  make  the  contractor 
responsible  for  any  needless  loss  of  water  or  gas. 

When  service  pipes  supplying  water  or  gas  to  adjoining 
houses  become  broken  during  excavation  or  other  work  the 
contractor  shall  repair  them  at  once  at  his  own  expense.  Delays 
such  as  would  result  in  adjoining  houses  having  to  go  over  night 
without  water  or  gas  or  for  a  needlessly  long  period  during  the 
day  will  not  be  tolerated.  The  engineer  reserves  the  right  to 
remedy  such  delays  or  neglect  by  ordering  outside  parties  to 
make  such  repairs  at  the  expense  of  the  contractor  and  without 
prior  notice. 

At  such  street-crossings  and  other  points  as  may  be 
directed  by  the  engineer  the  trenches  shall  be  bridged  in  a 
secure  manner,  so  as  to  prevent  any  serious  interruption  of 
travel  upon  the  roadway  and  sidewalks  and  also  to  afford 
necessary  access  to  public  and  private  premises.  The  mate- 
rial used  and  mode  of  constructing  such  bridges  and  the 
approaches  thereto  must  be  satisfactory  to  the  engineer;  the 
cost  of  all  such  work  must  be  included  in  the  regular  price  bid 
for  the  sewer.  (Crossings  should  not  be  tunnelled  under,  since 
it  is  almost  impossible  to  so  refill  the  tunnels  as  to  prevent  after- 


19°  SEWERAGE. 

settlement,  but  should  be  bridged.  Direct  access  to  the  street 
should  be  given  to  fire-engine  houses  and  usually  to  livery- 
stables.)  All  fire-hydrants  shall  be  left  uncovered  and  accessi- 
ble. The  contractor  shall  at  his  own  expense  provide  for  all 
watercourses,  gutters,  and  drains  interrupted  by  the  work, 
and  replace  them  in  as  good  condition  as  he  found  them. 

Paragraph  19.  Rock  Trenches. — When  the  excavation 
for  a  pipe  sewer  or  drain  is  made  through  rock  or  other 
material  too  hard  to  be  readily  or  conveniently  removed  for 
admitting  the  hubs  of  the  pipe  the  trench  shall  be  excavated 
at  least  4  inches  deeper  than  the  grade  of  the  outside  bottom 
of  the  pipe  and  [filled  with  concrete  up  to  and  around  such 
pipe,  as  shown  upon  the  plans]  [refilled  to  such  grade  with 
sand  or  other  suitable  material,  free  from  stones  or  other  hard  sub- 
stances, thoroughly  rammed].  When  rock  is  encountered  in  the 
trench  it  shall  be  stripped  of  earth  and  the  engineer  notified  and 
given  proper  time  to  measure  the  same  before  blasting.  No  rock 
removed  which  has  not  been  measured  by  the  engineer  will  be 
estimated  as  rock  excavation.  Measurement  for  rock  excavation 
will  be  limited  to  6  inches  on  either  side  of  the  sewer,  and  trench- 
slopes  of  8  vertical  to  i  horizontal.  In  all  cases  of  blasting  the 
blast  shall  be  carefully  covered  with  heavy  timbers  chained  together, 
rope  mat  or  by  some  other  equally  effective  method;  and  the 
engineer  may  limit  the  number  of  simultaneous  discharges. 
Local  laws  shall  be  observed  concerning  the  amount  of  explosives 
which  may  be  kept  on  hand  at  one  time  in  any  one  place,  and  con- 
cerning times  and  methods  of  handling  the  same  and  of  blasting. 
No  blasting  shall  be  done  within  20  feet  of  the  finished  sewer  or 
10  feet  of  an  uncovered  gas-  or  water-pipe,  and  the  end  of  the 
finished  sewer  shall  be  covered  or  stopped  with  plank  or  earth 
during  each  blast.  (If  the  sewer-end  is  not  so  protected  there 
is  a  possibility  of  stones  flying  into  the  sewer  and  also  of  the 
concussion  of  air  opening  the  joints.} 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.       191 


ART.  48.     CONSTRUCTION. 

Paragraph  20.  Foundations.  —  When  timber  or  pile 
foundations  other  than  those  shown  in  the  plans  are  neces- 
sary, in  the  opinion  of  the  engineer,  special  designs  will  be 
furnished  the  contractor,  who,  in  accordance  with  such 
designs,  shall  place  such  foundations  in  position  satisfactory 
to  the  engineer.  Planking  in  platforms  shall  be  laid  in  the 
manner  directed,  closely  joined,  and  each  plank  spiked  to  each 
cap  or  sill  with  nails  or  spikes  of  a  length  at  least  2  J  times  the 
thickness  of  the  plank.  If  cradles  or  platforms  are  laid 
directly  upon  the  ground  this  must  be  graded  perfectly  even 
and  smooth  to  receive  them  and  give  a  good  and  firm  bearing 
throughout.  If  caps  or  sills  are  used  the  spaces  between  them 
and  under  the  planking  must  be  filled  with  good  earth 
thoroughly  rammed. 

Where  piles  are  used  they  shall  be  driven  to  refusal,  unless 
extending  more  than  10  feet  below  the  foundation,  when  they 
shall  show  a  penetration  in  inches  under  the  final  blow  not 

greater  than  -j I,  in  which  L  is  the  weight  to  be  borne 

jL/ 

by  each  pile,  w  is  the  weight  of  the  hammer  in  pounds,  and 
h  its  fall  in  feet.  After  driving,  the  piles  shall  be  sawed  off 
truly  and  evenly  at  the  proper  elevation  for  receiving  the 
caps,  which  shall  be  fastened  to  them  with  i-inch  drift-bolts 
of  a  length  twice  the  depth  of  the  sill,  holes  for  such  bolts 
having  first  been  bored  with  a  -J-inch  bit.  If  any  pile  shall 
be  out  of  line  more  than  -J-  the  diameter  of  its  upper  end  the 
engineer  may  refuse  to  estimate  it  and  may  order  another 
driven  in  its  place. 

Concrete  or  stone-masonry  foundations  shall  be  con- 
structed where  ordered  in  a  manner  similar  to  that  specified 
for  "  Concrete  "  and  "  Stone  Masonry." 


192  SEWERAGE. 

Paragraph  21  A.  Concrete.— Concrete,  unless  otherwise 
specified,  shall  be  composed  of  i  bag  of  Portland  cement,  2\ 
cubic  feet  of  sand,  and  5  cubic  feet  of  broken  stone,  gravel,  or 
furnace-slag  of  approved  quality,  free  from  dust  and  dirt  and 
broken  so  as  to  pass  in  every  way  through  a  2-inch  ring.  All 
material  shall  be  actually  measured  for  each  batch,  in  specially 
prepared  boxes.  In  hand  mixing,  the  sand  shall  be  spread  out 
upon  a  suitable  platform  or  box  and  the  cement  deposited  upon 
this;  these  shall  then  be  thoroughly  mixed  dry  until  the  whole 
is  of  an  even,  uniform  color,  when  sufficient  clean  water  shall 
be  added  to  form  a  thick  paste.  The  stone,  which  has  previously 
been  thoroughly  wet,  shall  then  be  added  and  the  whole  shall  be 
quickly  and  thoroughly  mixed,  until  every  stone  is  coated  with 
mortar,  water  being  gradually  added  by  sprinkling,  if  necessary, 
to  obtain  a  better  consistency.  If  mixing  be  done  by  machinery 
the  mixer  employed  shall  permit  of  actually  measuring  materials 
and  of  producing  a  thorough  mixture  of  the  same.  Whether  hand 
or  machine  mixing  be  employed,  the  mixing  shall  be  as  thorough 
is  practically  obtainable. 

Concrete  must  not  be  mi^ed  in  quantities  greater  than  required 
for  immediate  use,  and  any  which  has  begun  to  set  shall  not  be 
retempered  or  used  in  any  way.  Concrete  shall  be  mixed  suffi- 
ciently wet  to  settle  to  place  against  the  forms  by  light  ramming, 
which  shall  bring  water  to  the  surface.  The  forms  shall  be 
sufficiently  tight  to  prevent  leakage  of  water  through  them. 
Where  fresh  concrete  is  to  be  placed  in  contact  with  that  already 
set  or  partly  set  all  loose  stone  or  concrete  not  thoroughly  com- 
pacted shall  be  removed  from  the  surface  of  the  latter,  which 
shall  be  washed  clean  of  all  dirt  and  given  a  thin  coat  of  mortar. 
If  such  a  surface  be  hard  set  it  shall  previously  be  thoroughly 
water-soaked.  When  concrete  is  in  place  all  wheeling,  working, 
or  walking  on  it  must  be  prevented  until  it  is  firmly  set,  and 
until  such  time  it  shall  be  kept  damp  and  protected  from  the 
sun. 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.        193 

Such  forms  and  centres  as  may  be  necessary  to  give  the 
finished  concrete  the  desired  form  shall  be  furnished  by  the 
contractor  without  extra  charge.  These  shall  be  sufficiently 
stiff  and  substantial  to  retain  the  concrete  firmly  in  place,  and 
shall  not  be  withdrawn  until  the  same  has  set  to  the  satisfac- 
tion of  the  engineer.  No  concrete  shall  be  made  or  used  when 
the  temperature  is  below  30°  Fahr.  without  the  permission  of 
the  engineer,  whose  instructions  and  restrictions  for  such  use 
.shall  be  followed. 

Paragraph  21  B.  Concrete.  (Specifications  Proposed  in 
1909  by  the  National  Association  of  Cement  Users.)  Fine  aggre- 
gate shall  consist  of  sand,  crushed  stone,  or  gravel  screenings, 
graded  from  fine  to  coarse,  passing  when  dry  a  screen  having  J-inch 
diameter  holes;  shall  be  of  siliceous  materials,  clean,  coarse> 
free  from  vegetable  loam  or  other  deleterious  matter,  and  not 
more  than  6  per  cent  shall  pass  a  sieve  having  100  meshes  per 
linear  inch. 

Mortars  composed  of  one  part  Portland  cement  and  three 
parts  fine  aggregate  by  weight  when  made  into  briquettes  shall 
show  a  tensile  strength  of  at  least  70  per  cent  of  the  strength  of 
1:3  mortar  of  the  same  consistency  made  with  the  same  cement 
.and  standard  Ottawa  sand. 

Coarse  aggregate  shall  consist  of  inert  material,  graded  in 
size,  such  as  crushed  stone,  or  gravel,  which  is  retained  on  a 
screen  having  J-inch  diameter  holes;  shall  be  clean,  hard, 
durable,  and  free  from  all  deleterious  materials.  Aggregates 
containing  soft,  flat  or  elongated  particles  shall  be  excluded. 

The  maximum  size  of  the  coarse  aggregate  shall  be  such  that 
it  will  not  separate  from  the  mortar  in  laying  and  will  not  prevent 
the  concrete  fully  filling  all  parts  of  the  forms.  The  size  of  the 
coarse  aggregate  shall  be  such  as  to  pass  a  f -inch  ring. 

Where  cinder  concrete  is  permissible  the  cinders  used  as  the 
coarse  aggregate  shall  be  composed  of  hard,  clean,  vitreous 
clinker,  free  from  sulphides,  unburned  coal  or  ashes. 


194  SEWERAGE. 

Water  shall  be  clean,  free  from  oil,  acid,  strong  alkalies,  or 
vegetable  matter. 

The  concrete  shall  be  so  proportioned  that  the  cement  shall 
overfill  the  voids  in  the  fine  aggregate  by  at  least  five  per  cent  (5%), 
and  the  mortar  shall  overfill  the  voids  in  the  coarse  aggregate 
by  at  least  ten  per  cent  (10%).  The  proportions  shall  not  exceed 
one  (i)  part  of  cement  to  eight  (8)  parts  of  the  fine  and  coarse 
aggregates. 

When  the  voids  are  not  determined,  the  concrete  shall  have 
the  proportions  of  one  (i)  part  cement,  three  (3)  parts  fine 
aggregates  and  five  (5)  parts  coarse  aggregates.  A  sack  of 
cement  (94  pounds)  shall  be  considered  to  have  a  volume  of 
one  (i)  cubic  foot. 

The  ingredients  of  concrete  shall  be  thoroughly  mixed  to  the 
desired  consistency,  and  the  mixing  shall  continue  until  the 
cement  is  uniformly  distributed  and  the  mass  is  uniform  in  color 
and  homogeneous,  since  maximum  density  and  therefore  greatest 
strength  of  a  given  mixture  depends  largely  on  thorough  and 
complete  mixing. 

a.  Measuring  Proportions. — Methods  of  measurement  of  the 
proportions  of  the  various  ingredients,  including  the  water,  shall 
be  used,  which  will  secure  separate  uniform  measurements  at 
all  times. 

b.  Machine    Mixing. — When    the    conditions  will  permit,   a 
machine  mixer  of  a  type  which  insures  the  proper  proportioning 
of  i.he  materials  throughout  the  mass  shall  be  used,  since  a  more 
thorough  and  uniform  consistency  can  be  thus  obtained. 

c.  Hand  Mixing. — When   it  is  necessary  to   mix  by  hand, 
the  mixing  shall  be  on  a  water-tight  platform  and  especial  pre- 
cautions shall  be  taken  to  turn  the  materials  until  they  are  homo- 
geneous in  appearance  and  color. 

d.  Consistency. — The   materials   shall   be   mixed   wet  enough 
to  produce    a  concrete  of  such  a  consistency  as  will  flow  into 
the    forms    and    about    the    metal    reinforcement,    and  which, 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.       195 

on  the  other  hand,  can  be  conveyed  from  the  mixer  to  the 
forms  without  separation  of  the  coarse  aggregate  from  the 
mortar. 

e.  Retempering.- — Retempering  mortar  or  concrete,  i.e.,  re- 
mixing with  water  after  it  has  partially  set,  will  not  be  per- 
mitted. 

/.  Methods.— Concrete,  after  the  addition  of  water  to  the 
mix,  shall  be  handled  rapidly,  and  in  as  small  masses  as  is 
practicable  from  the  place  of  mixing  to  the  place  of  final  deposit, 
and  under  no  circumstances  shall  concrete  be  used  that  has 
partially  set  before  final  placing.  A  slow-setting  cement  should 
be  used  when  a  long  time  is  liable  to  occur  between  mixing  and 
final  placing. 

When  work  is  resumed,  concrete  previously  placed  shall 
be  roughened,  thoroughly  cleaned  of  foreign  material  and 
laitance,  drenched  and  slushed  with  a  mortar  consisting  of 
one  part  Portland  cement  and  not  more  than  two  parts  fine 
aggregate. 

The  faces  of  concrete  exposed  to  premature  drying  shall  be 
kept  wet  for  a  period  of  at  least  seven  days. 

g.  Freezing  Weather. — The  concrete  shall  not  be  mixed  or 
deposited  at  a  freezing  temperature  unless  special  precautions 
are  taken  to  avoid  the  use  of  materials  containing  frost  or  covered 
with  ice  crystals,  and  in  providing  means  to  prevent  the  concrete 
from  freezing  after  being  placed  in  position  and  until  it  has 
thoroughly  hardened. 

Paragraph  22.  Stone  and  Brick  Masonry. — Stone  and 
brick  masonry,  unless  otherwise  specified,  shall  be  laid  with 
mortar  composed  of  i  part  by  measure  of  Portland  cement  to 
3  of  sand,  mixed  as  specified  for  concrete  mortar.  No  mortar 
shall  be  used  after  it  has  set  or  partially  set. 

Stone  masonry  must  be  laid  true  and  by  line  and  built  of 
the  exact  dimensions  shown  in  the  plans  of  the  work.  All 
stones  shall  be  laid  upon  their  natural  beds  and  roughly 


JQ6  SEWERAGE. 

.squared  on  the  joints,  beds,  and  faces,  the  stone  breaking 
joints  at  least  6  inches,  and  with  at  least  one  header  for  every 
three  stretchers.  Headers  shall  be  at  least  3  feet  long  or 
extend  entirely  through  the  wall.  No  stone  once  bedded 
shall  be  lifted  by  spalling,  but  any  spalls  used  must  be  em- 
bedded in  the  mortar  before  setting  the  stone.  Each  stone 
shall  be  floated  to  place  in  a  full  bed  of  mortar  and  every 
joint  thoroughly  filled  with  the  same.  No  dressing  of  stone 
upon  the  wall  will  be  allowed.  (For  river-  or  retaining- walls 
further  specifications  should  be  added  as  to  thickness  of  joints, 
character  of  face  dressing,  etc.} 

For  brick  masonry  in  straight  walls  or  sewers  none  but 
whole,  sound  brick  shall  be  used.  For  manholes,  flush-tanks, 
and  similar  work  a  limited  number  of  half  brick  may  be  used, 
not  to  exceed  J-  of  the  whole  in  any  case.  Unless  the  engineer 
direct  otherwise  each  brick  shall  be  thoroughly  wetted  imme- 
diately before  being  laid.  (If  the  brick  absorbs  practically  no 
water  this  wetting  should  be  omitted,  as  likely  to  cause  the  brick 
to  slide  on  the  mortar  and  cause  uneven  work.)  It  shall  be  laid 
with  a  full,  close  joint  of  cement  mortar  on  its  bed,  ends,  and 
:side  at  one  operation.  In  no  case  is  mortar  to  be  slushed  in 
afterward.  Special  care  shall  be  taken  to  make  the  face  of 
the  brick-work  smooth,  and  all  joints  on  the  interior  of  a 
sewer  shall  be  carefully  struck  with  the  point  of  a  trowel  or 
pointed  to  the  satisfaction  of  the  engineer.  Where  pipe- 
connections  enter  a  sewer  or  manhole  "  bull's-eyes  "  shall  be 
constructed  by  laying  rowlock  courses  of  brick  around  them, 
the  cost  of  such  construction  being  included  in  the  regular 
price  bid  for  the  sewer  or  appurtenance.  Around  pipe  more 
than  15  inches  in  diameter  2  rowlock  courses  shall  be  laid. 

Brick-work  in  sewers  shall  be  laid  by  line,  each  course 
perfectly  straight  and  parallel  to  the  axis  of  the  sewer.  Joints 
appearing  in  the  sewer  shall  in  no  case  exceed  i  inch  in  width. 
Sewers  shall  conform  accurately  in  section  and  dimensions  to 


SPECIFICATIONS,  CONTRACT,  ESTIMATE    OF   COST.       197 

the  plans  of  the  same.  All  inverts  and  bottom  curves  shall 
be  worked  from  templets  accurately  set,  the  arches  are  to  be 
formed  upon  strong  centres  accurately  and  solidly  set,  and  the 
crowns  keyed  in  full  joints  of  mortar.  No  centres  shall  be 
drawn  until  the  arch  masonry  has  set  to  the  satisfaction  of  the 
engineer  and  refilling  progressed  up  to  the  crown.  They 
shall  be  drawn  with  care,  so  as  not  to  crack  or  injure  the  work. 
The  extrados  is  to  be  neatly  plastered  with  cement  mortar  J 
inch  thick,  the  arches  being  cleaned  and  wetted  just  before 
plastering.  Where  brickwork  is  left  and  is  to  be  joined  to  new 
work,  it  shall  be  racked  back  in  courses,  and  toothing  shall  not  be 
allowed  except  by  consent  of  the  engineer.  Before  beginning  the 
succeeding  section  all  loose  brick  at  the  end  shall  be  removed 
and  the  faces  cleaned  of  mortar.  All  brickwork  shall  be  thor- 
oughly bonded,  adjacent  courses  breaking  joints  at  least  one- 
third  the  exposed  length  of  the  brick. 

Stone  blocks  and  paving  brick,  when  used,  shall  be  laid  in 
Portland-cement  mortar  composed  of  equal  parts  by  measure 
of  cement  and  sand.  Joints  shall  not  exceed  f  inch  in  width. 
The  face  of  the  masonry  shall  be  such  that  there  shall  be  no 
projection  beyond  the  general  surface  exceeding  -J-  inch.  All 
joints  shall  be  cleaned  out  to  a  depth  of  J  inch  and  pointed  with 
neat  Portland-cement  mortar.  All  stone-block  work  shall  be 
laid  in  other  respects  as  specified  for  brick-work. 

If  there  should  be  any  distortion  of  the  sewer  before  accept- 
ance this  shall  be  corrected  by  tearing  down  and  rebuilding. 
No  local  patching  will  be  allowed,  but  when  repairs  are  necessary 
a  section  shall  be  removed  at  least  3  feet  long  and  including  the 
entire  arch,  or  the  entire  sewer  if  the  defect  is  in  the  invert. 
Leakage  of  ground-water  into  the  sewer  shall  be  similarly 
corrected,  unless  it  can  be  prevented  by  calking  the  joints  with 
oakum  saturated  in  cement,  with  wooden  plugs,  or  other  mate- 
rial acceptable  to  the  engineer. 

When  work  is  done  during  freezing  weather,  the  contractor 


198  SEWERAGE. 

shall  provide  the  necessary  means  for  heating,  and  shall  heat 
the  bricks,  gravel,  stone,  sand  and  water,  and  shall  comply  with 
all  requirements  of  the  engineer  to  protect  thoroughly  the 
masonry  from  damage  during  and  after  laying,  all  at  the  cost 
and  expense  of  the  contractor.  No  work  shall  be  done  on 
masonry  during  such  days  when,  in  the  opinion  of  the  engineer, 
good  work  cannot  be  done.  All  unfinished  masonry  shall  be 
properly  protected  during  inclement  weather  from  injury  by 
water  or  frost. 

Paragraph  23.  Concrete  Sewer  built  in  Place. — Concrete 
sewer,  if  constructed  within  the  trench,  shall  be  of  the  sections 
shown  on  the  drawings.  Great  care  shall  be  taken  to  keep 
the  forms  free  from  earth  and  other  foreign  material,  and  to 
prevent  admixture  of  foreign  materials  with  the  concrete  while 
placing.  A  tight  sewer  barrel  and  a  hard,  smooth  invert  will 
be  required.  This  must  be  attained  as  far  as  possible  without 
plastering  or  pointing. 

Voids  must  be  promptly  repaired.  If  necessary,  voids  shall 
be  repaired  by  cutting  out  a  portion  of  the  finished  work  and 
replacing  with  new  work. 

Where  reinforcement  is  called  for  the  steel  rods  shall  be 
placed  accurately  in  the  positions  shown  on  the  drawings  or 
ordered,  and  shall  be  bent  to  the  proper  shapes  before  being 
placed.  They  shall  be  wired  together  at  intersections  where 
shown  or  necessary.  Adjoining  rods  shall  lap  at  least  6  inches. 

The  centres  and  forms  for  all  faces  which  will  be  exposed 
in  the  finished  work  shall  be  smooth  and  prepared  or  covered 
in  a  manner  satisfactory  to  the  engineer,  so  that  they  may  be 
readily  removed  and  leave  the  concrete  with  a  smooth,  present- 
able surface.  All  centres  and  forms  shall  be  of  sufficient  strength 
and  well  braced  so  that  they  will  maintain  their  proper  position 
during  the  placing  and  ramming  of  the  concrete.  Special  centres 
and  forms  shall  be  provided  when  required.  No  centre  or  form 
shall  be  used  which  is  not  clean,  of  proper  shape  and  strength 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.       199 

and  in  every  way  suitable.  Deformed,  broken  or  defective  centres 
or  forms  shall  be  removed  from  the  work.  No  centres  or  forms 
in  any  part  of  the  work  shall  be  struck  without  the  consent  of 
the  engineer. 

Where  new  work  is  joined  to  old,  a  bed  of  mortar  one  (i)  inch 
thick,  composed  of  one  (i)  volume  of  cement  and  one  (i)  volume 
of  sand  shall  be  used  to  secure  a  bond  between  the  surfaces. 
Before  placing  this  mortar  the  surface  of  the  old  work  shall  be 
thoroughly  washed  clean  of  all  adhering  substances. 

All  exposed  surfaces  of  finished  or  unfinished  work  shall  be 
kept  constantly  moist  by  sprinkling  with  clean  water  at  short 
intervals,  unless  otherwise  directed  during  cold  weather,  or  by 
covering  with  moistened  burlap,  or  by  such  other  means  as  shall 
be  approved,  and  this  moistening  shall  be  continued  until  the 
permanent  covering  is  in  place  or  until,  in  the  opinion  of  the 
engineer,  the  concrete  has  sufficiently  hardened.  The  con- 
tractor shall  not  permit  walking  upon  the  concrete  until  it  has 
set  for  a  sufficient  length  of  time,  to  be  determined  by  the 
engineer. 

Should  any  voids  or  other  defects  be  discovered  in  any  part 
of  the  work  when  the  forms  are  taken  down,  or  otherwise,  the 
defective  work  shall  be  removed  and  the  space  refilled  with  suit- 
able material  in  a  proper  manner,  at  the  expense  of  the  con- 
tractor. 

Paragraph  24.  Laying  Pipe  Sewers. — Previous  to  being 
lowered  into  the  trench  each  pipe  shall  be  carefully  inspected, 
and  those  not  meeting  the  foregoing  specifications  shall  be 
rejected,  and  either  destroyed  or  removed  from  the  work 
within  10  hours;  except  that  pipe  suitable  for  sub-drains  may 
be  used  for  that  purpose,  but  shall  be  kept  apart  from  the 
sewer-pipe.  All  lumps  or  excrescences  on  the  ends  of  each 
pipe  shall  be  removed  before  it  is  lowered  into  the  trench. 
No  pipe  shall  be  laid  except  in  the  presence  of  the  engineer 
or  his  authorized  inspector,  and  the  engineer  may  order  the 


200  SEWERAGE. 

removal  and  relaying  of  any  pipe  not  so  laid.  The  trench 
shall  be  excavated  in  accordance  with  Paragraphs  14  and  19. 
No  sewers  shall  be  laid  within  10  feet  of  the  excavating  or  40 
feet  of  the  blasting.  Pipes  having  any  defects  which  do  not 
cause  their  rejection  shall  be  so  laid  as  to  bring  these  in  the 
top  half  of  the  sewer,  and  if  the  bell  or  spigot  be  broken  the 
defective  place  must  be  liberally  covered  with  neat  cement 
mortar,  reinforced  with  a  piece  of  pipe  or  pipe-ring  if  the 
engineer  so  direct. 

The  pipes  and  specials  shall  be  so  laid  in  the  trench  that 
after  the  sewer  is  completed  the  interior  surface  thereof  shall 
conform  accurately  to  the  grades  and  alignment  fixed  and 
given  by  the  engineer.  All  adjustment  to  line  and  grade  of 
pipes  laid  directly  upon  the  bottom  must  be  done  by  scraping 
away  or  filling  in  the  earth  under  the  body  of  the  pipe,  and 
not  by  blocking  or  wedging  up.  Before  laying,  the  interior 
of  the  bell  shall  be  carefully  wiped  smooth  and  clean,  and  the 
annular  space  shall  be  free  from  dirt,  stones,  or  water.  A 
narrow  gasket  of  packing  dipped  in  cement  grout  shall  be 
properly  calked  into  each  joint,  after  which  cement  mortar  shall 
be  introduced  therein.  Such  gasket  shall  be  in  one  piece,  of 
sufficient  length  to  reach  entirely  around  the  pipe  and  of  a 
thickness  sufficient  to  bring  the  bottoms  of  the  two  pipes  to  the 
same  level.  No  joint  shall  be  cemented  until  the  gaskets  of 
the  next  two  joints  in  advance  are  properly  inserted.  Special 
care  must  be  taken  to  properly  fill  with  mortar  the  annular  space 
at  the  bottom  and  sides  as  well  as  at  the  top  of  the  joints.  After 
such  space  has  been  filled,  a  neat  finish  shall  be  given  to  the 
joint  by  the  further  application  of  similar  mortar  to  the  face 
of  the  hub  so  as  to  form  a  continuous  and  even  bevelled  surface 
from  the  exterior  of  said  hub  to  the  exterior  of  the  spigot  all 
around.  All  water  must  be  kept  out  of  the  bell-hole  during 
laying,  or  else  such  bell-hole  must  be  competely  filled  out  with 
the  cement  mortar  specified  or  with  concrete,  for  which  mortar 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.     201 

or  concrete  no  extra  compensation  will  be  allowed.  The  interior 
of  the  joint  shall  be  wiped  clean  of  cement  by  a  wad  made  of 
a  sack  rilled  with  hay,  large  enough  to  tightly  fill  the  pipe  and 
attached  to  a  rod  or  cord,  which  shall  at  all  times  be  kept  in 
the  sewer  and  pulled  ahead  past  each  joint  as  soon  as  it  is 
cemented;  or  by  other  method  which  is  satisfactory  to  the 
engineer.  The  mortar  used  shall  be  composed  of  [i  part  Port- 
land cement  to  i  of  sand]  [neat  Portland  cement]  wet  to  a  thick 
paste.  (Engineers  do  not  agree  as  to  the  advisability  of  using 
neat-cement  mortar.  Experiment  seems  to  show  that  natural  cement 
gives  a  tighter  joint  if  mixed  with  sand,  Portland  if  used  neat.) 

As  soon  as  the  cementing  of  any  joint  has  been  completed 
the  bell-hole  under  the  hub  must  be  carefully  and  compactly 
filled  with  sand,  loam,  or  fine  earth,  so  as  to  hold  the  external 
mortar  finish  of  said  joint  securely  in  its  place.  Refilling 
shall  also  be  made  with  selected  material,  free  from  stones, 
carried  halfway  up  the  sides  or  circumference  of  the  entire 
length  of  pipe  and  compacted  with  a  proper  tamping-tool. 
The  trench  shall  then  be  filled  to  a  point  at  least  2  feet  above 
the  top  of  the  pipe  with  material  containing  no  stone  larger 
than  2  inches  in  any  dimension. 

While  the  pipes  and  specials  are  being  laid  in  each  section 
between  manholes  or  other  permanent  openings  light  from  the 
remote  end  of  the  section  shall  remain  constantly  in  plain  view 
throughout  the  entire  length  of  such  section  or  division. 
Sections  between  openings  will  in  general  not  exceed  300  to 
400  feet;  in  particular  cases  the  distance  may  be  somewhat 
greater. 

Practically  water-tight  work  is  required  in  both  lateral  and 
street  sewers,  and  the  engineer  will  carefully  test  the  sewers  to. 
determine  the  amount  of  leakage  of  ground  water  into  sewers 
during  wet  weather.  During  very  wet  weather  the  total  infiltra- 
tion of  ground  water  into  the  whole  system  shall  not  exceed  one 
gallon  per  twenty-four  hours  per  foot  of  street  sewer,  and  the 


202  SEWERAGE. 

leakage  into  any  section  between  adjacent  manholes,  including 
that  at  the  manholes,  shall  not  exceed  6  gallons  per  twenty-four 
hours  per  lineal  foot  of  street  sewer.  After  the  sewers  have  been 
completed  and  the  trenches  backfilled  the  engineer  will  measure 
the  leakage  of  ground  water  into  the  sewers,  and  should  this 
leakage  exceed  in  amount  thirty  thousand  (30,000)  gallons  in 
twenty-four  (24)  hours  per  mile  in  length  of  sewer,  the  contrac- 
tor shall,  at  his  own  expense,  repair  the  sewers  by  calking  or 
otherwise,  so  that  the  leakage  shall  not  exceed  the  amount  specified 
above.  The  contractor  shall,  at  his  own  expense,  build  bulk- 
heads and  weirs  and  furnish  the  engineer  such  labor  and  materials 
as  may  be  necessary  to  conduct  these  measurements. 

At  such  places  as  will  be  directed  by  the  engineer,  branches 
will  be  inserted  in  the  sewer  for  future  connections.  Each 
branch  thus  inserted  shall  be  closed  by  a  thin  vitrified  stone- 
ware cover  or  plug,  which  shall  be  placed  before  the  special 
pipe  is  lowered  into  the  trench.  The  covers  shall  be  so  inserted 
and  cemented  in  as  to  prevent  any  water  entering  the  sewer, 
at  any  time  before  their  removal,  through  such  branches.  The 
entire  cost  of  furnishing  and  setting  such  covers  shall  be  included 
in  the  regular  price  bid  for  branches.  Where  directed  by  the 
engineer  deep-cut  connections  shall  be  constructed  as  shown 
upon  the  plans. 

Any  omission  of  the  required  branches,  manholes,  lamp- 
holes,  or  other  special  constructions  indicated  upon  the  plans, 
or  that  may  be  specially  ordered  beforehand  by  the  engineer, 
shall  be  corrected  by  the  contractor  at  his  own  expense. 

Before  leaving  the  work  for  the  night  or  at  any  other  time 
the  end  of  the  sewer  shall  be  securely  closed  with  a  tight- 
fitting  plug. 

Paragraph  25.  Laying  Sub-drains. — Sub-drains  shall  be 
laid  in  sub-trenches  excavated  of  the  dimensions  and  in  the 
location  shown  upon  the  plans,  and  of  such  depth  as  is  neces- 
sary to  lay  the  pipe  at  the  grade  given  by  the  engineer.  This 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.      203 

sub-trench,  if  in  unstable  material,  shall  be  filled  with  clean 
broken  stone  or  gravel,  not  less  than  \  inch  nor  more  than 
i  inch  in  any  dimensions,  up  to  the  drain  invert;  this  broken 
stone  or  gravel  being  solidly  compacted,  so  that  there  may 
be  no  future  settlement.  On  this  the  drain-pipe  shall  be 
laid  accurately  to  grade,  having  first  been  inspected  and  all 
pipe  not  meeting  the  specifications  having  been  rejected.  A 
piece  of  cheese-cloth  or  similar  material  satisfactory  to  the 
engineer,  at  least  5  inches  wide  and  twice  as  long  as  the  out- 
side circumference  of  the  pipe,  shall  be  laid  on  the  broken 
stone  with  its  centre  under  the  joint  between  two  pipes;  first 
one  end  and  then  the  other  of  this  shall  be  carried  over  the 
pipes  and  under  the  opposite  side,  care  being  taken  to  keep 
the  cloth  spread  out  and  its  centre  over  the  joint.  The  pipes 
shall  be  separated  by  a  space  of  about  J  inch.  The  space 
between  the  pipes  and  the  sides  of  the  sub-trench  shall  then 
be  carefully  filled  with  broken  stone  or  gravel  as  specified 
above,  carefully  compacted,  which  material  shall  be  similarly 
placed  to  a  depth  of  6  inches  above  the  pipe.  Where  directed 
by  the  engineer  this  stone-filling  shall  be  covered  by  hemlock 
plank,  to  be  paid  for  as  "  timber  in  foundations."  If  any 
earth  or  other  material  shall  fall  into  the  sub-trench  while  the 
laying  of  stone  filling  is  proceeding,  such  material  and  the 
adjacent  stone-filling  shall  be  removed  and  clean  stone  be  put 
in  its  place. 

Where  directed  by  the  engineer  branches  shall  be  inserted 
in  the  sub-drain  for  future  connections.  These  shall  be  closed 
as  specified  for  sewer  branches,  and  the  specification  as  to  the 
omission  of  sewer  specials  shall  apply  to  sub-drain  specials 
also. 

Paragraph  26.  Regular  Appurtenances. — Manholes  of 
the  various  kinds — line,  intersection,  drop,  etc. — lamp-holes, 
flush-tanks,  inlets,  and  other  appurtenances  shall  be  built 
where  the  engineer  may  direct,  in  size,  form,  thickness,  and 


204  SEWERAGE. 

all  other  respects  in  accordance  with  the  plans,  but  manholes 
whose  height  exceeds  12  feet  shall  have  walls  12  inches  thick 
below  that  depth.  All  appurtenances  shall  be  brought  up 
accurately  to  the  grade  given  by  the  engineer.  Great  care 
shall  be  taken  to  make  the  channels  in  manholes  and  lamp- 
holes  conform  accurately  to  the  sewer  grade.  In  the  case  of 
pipe-sewers  split  pipe  shall  be  used  for  the  inverts  to  these 
channels  where  possible.  Where  a  curve  in  the  channel  or 
some  other  condition  prevents  this  the  channel  shall  be  formed 
of  bricks  on  edge,  set  in  Portland-cement  mortar.  Brick 
channels  shall  be  lined  with  neat  Portland-cement  mortar  J 
inch  thick,  and  the  inverts  shall  be  exactly  semi-circular  of  the 
diameter  of  the  pipes  which  they  connect.  If  these  be  of 
different  diameters  the  channel  shall  taper  uniformly  from  one 
size  to  the  other.  The  outsides  of  manholes  shall  be  plastered 
with  J-inch  of  cement  mortar. 

Flush-tanks  and  inlets  shall  be  plastered  on  the  outside 
with  \  inch  of  cement  mortar;  and  on  the  inside  shall  be  given 
three  coats  of  thin  Portland-cement  grout,  without  sand, 
applied  with  a  brush,  each  coat  being  allowed  to  set  before 
the  next  is  applied.  (This  will  be  more  certain  to  make  a 
water-tight  construction  than  plastering  with  mortar.} 

Care  shall  be  taken  to  place  the  inlet  tops,  when  these  are 
in  the  sidewalk,  exactly  in  line  with  the  curb,  and  to  place 
the  bottoms  of  the  openings  or  the  gratings  exactly  on  the 
gutter  grade  given. 

All  manholes  and  flush-tanks  shall  be  fitted  with  steps 
similar  to  those  shown  on  the  plans,  and  spaced  15  inches 
,-\part  vertically.  All  tops  or  other  fittings  shall  be  set  during 
the  construction  or  at  the  completion  of  each  appurtenance, 
in  a  firm,  neat,  and  workmanlike  manner. 

All  concrete,  stone,  or  brick  masonry  shall  conform  to  the 
specifications  given  in  Paragraphs  21  and  22.  Each  appurte- 
nance shall  be  begun  within  24  hours  of  the  time  it  is  reached 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.        205 

in  the  laying  of  the  sewer,  and   shall  be  completed  and  the  exca- 
vation closed  as  expeditiously  as  possible. 

When  automatic  flushing  apparatus  is  furnished  by  the  con- 
tractor, he  shall  set  it  and  establish  it  in  good  operating  condition. 
He  shall  at  his  expense  furnish  and  make  all  connections  to  the 
flush  tanks  from  adjoining  water  mains  in  a  satisfactory  manner; 
and  set  in  place  properly  all  necessary  siphon,  regulating,  feeding, 
overflow  and  vent  pipes,  lamp  holes,  stopcocks  and  devices. 
Siphons  shall  be  set  in  a  mass  of  concrete.  The  connections  to 
the  nearest  water  main,  averaging  not  over  40  feet,  shall  be  below 
the  frost  line  and  of  J-inch  galvanized  iron  pipe  with  suitable 
stopcock.  The  tapping  of  the  water  main  shall  be  at  the 
expense  of  the  contractor. 

ART.  49.  BACK-FILLING  AND  CLEANING  UP. 

Paragraph  27  a.  Back-filling.  —  In  back-filling  sewer- 
trenches  loose,  fine  earth,  free  from  stones,  shall  be  used  up  to 
a  point  2  feet  above  the  sewer,  and  shall  be  thoroughly  com- 
pacted in  6-inch  layers  with  shovels  or  wooden  hand-rammers 
weighing  about  2  pounds  per  square  inch  of  face.  The  remainder 
of  the  trench  shall  contain  not  more  than  one-third  broken  rock,  and 
no  stone  of  this  shall  weigh  more  than  50  pounds.  If  necessary  to 
meet  this  requirement,  in  the  opinion  of  the  engineer,  the  con- 
tractor shall  supply  suitable  material  for  back-filling,  to  be  paid 
for  at  the  rate  bid  for  such  material.  The  filling  of  the 
trench  above  the  level  of  2  feet  above  the  sewer  shall  be 
rammed  in  p-inch  layers,  or,  when  directed  by  the  engineer, 
the  trenches  shall  be  water-tamped.  Water-tamping  shall  be 
done  in  each  case  as  directed  by  the  engineer.  All  back-fill- 
ing shall  be  done  by  hand  and  in  no  case  shall  scrapers  or 
ploughs  be  used.  In  back-filling  of  tunnels  or  under  railroad 
tracks  especial  care  shall  be  taken  to  thoroughly  compact  the 
material.  (The  question  of  back-filling  is  a  very  troublesome 


206  SEWERAGE. 

one.  In  most  soils,  when  the  diameter  of  the  sewer  does  not 
exceed  one  tenth  of  the  depth  of  the  trench,  all  the  earth 
excavated  can  be  returned  without  leaving  any  ridge  and  with- 
out any  appreciable  after-settlement.  But  this  can  be  done  only 
at  c  nsiderable  expense — from  4.  to  12  cents  for  each  cubic  yard 
of  back-filling — by  careful  ramming  or  water-tamping;  in  tough 
clay  no  way  has  yet  been  found  to  accomplish  this.  When  the 
trench  is  through  fields  or  unpaved  streets  this  extra  payment  is 
not  generally  warranted  by  the  benefits  derived;  but  through 
paved  streets  it  generally  is.  The  above  specifications  are 
similar  to  those  ordinarily  used,  but  contractors  generally 
understand  that  they  vvill  not  be  enforced  except  in  well-paved 
streets,  and  bid  accordingly.  It  is  preferable  to  leave  the  option 
confessedly  with  the  engineer  as  to  whether  the  trench  shall  be 
tamped,  and  pay  for  the  tamping  which  is  ordered,  having  it 
well  done.  The  following  specification  is  offered  as  a  substitute, 
to  be  rigidly  enforced.) 

Paragraph  27.  b.  Back-filling. — In  back-filling  sewer- 
trenches  loose,  fine  earth,  free  from  stones,  shall  be  used  up  to 
a  point  2  feet  above  the  sewer,  and  shall  be  thoroughly  com- 
pacted in  4-inch  layers  by  hand-rammers,  there  being  four  rammers 
to  each  shoveller.  Rammers  for  this  purpose  shall  be  of  wood, 
shall  weigh  from  4  to  6  pounds  each,  and  have  not  to  exceed  4 
square  inches  of  face.  The  remainder  of  the  trench  shall  con- 
tain not  more  than  one-third  broken  rock,  and  no  stone  of  this 
shall  weigh  more  than  50  pounds.  If  necessary  to  meet  this 
requirement  the  contractor  shall  supply  .suitable  material  for 
back-filling.  Unless  otherwise  specified  the  trench  above  the 
level  of  2  feet  above  the  sewer  shall  be  filled  by  hand  with  this 
material  up  to  within  i  foot  of  the  surface,  and  the  remainder 
of  the  filling  shall  be  made  of  fine  material  containing 
no  stone  having  any  dimensions  greater  than  2  inches. 
The  filling  shall  be  crowned  above  the  trench,  having  a 
height  above  the  street  surface  of  one-twelfth  the  top  width 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.       207 

of  the  trench,  and  neatly  rounded  off,  the  paving  mate- 
rial previously  removed,  if  any,  being  spread  evenly  over 
the  top.  After  refilling,  and  for  6  months  after  the  comple- 
tion of  this  contract,  the  contractor  shall  from  time  to  time 
refill  any  settlements  which  may  occur,  constantly  maintaining 
the  trench  in  a  neat  and  safe  condition,  and  deliver  it  over  in 
that  condition  at  the  end  of  that  time.  Hand-ramming  or 
water-tamping  shall  be  used  where  directed,  and  as  follows, 
an  additional  sum  being  paid  therefor  according  to  the  price  bid. 

For  hand-ramming  the  earth  shall  be  spread  by  shovels  in 
4-inch  horizontal  layers  and  solidly  compacted  with  rammers 
weighing  from  10  to  20  pounds  and  having  a  face  of  not  to 
exceed  36  square  inches.  There  shall  be  three  rammers  to 
every  shoveller,  and  the  former  shall  be  of  at  least  as  great 
strength  and  efficiency  as  the  latter.  The  paving  shall  be 
restored  in  as  good  condition  as  found,  being  given  a  crown 
of  J  inch  over  the  trench  in  the  case  of  macadam  or  gravel  pav- 
ing, but  not  overlapping  the  old  paving.  During  back-filling 
no  sheathing  which  is  to  be  drawn  shall  at  any  time  ex- 
tend into  earth  which  is  being  rammed,  but  it  shall  be 
drawn  so  as  to  be  always  above  it,  if  it  cannot  be  at  once 
•entirely  removed. 

For  water-tamping  the  earth  shall  be  levelled  off  in  hori- 
zontal layers  2  feet  thick  and  flooded  with  water  until,  after 
standing  for  5  minutes,  water  shall  just  show  on  the  surface, 
when  another  layer  shall  be  thrown  in  and  flooded.  This 
shall  be  continued  up  to  within  2  feet  of  the  surface  and  allowed 
to  stand  for  a  few  hours.  The  last  2  feet  shall  then  be  put  in 
and  hand-rammed  as  specified  above,  and  the  paving  relaid. 

No  water  shall  be  turned  into  the  trench  until  all  cement- 
work  in  sewers  and  appurtenances  shall  have  had  full  time  to 
set.  (Water-tamping  is  especially  applicable  where  there  is 
much  stone  or  broken  rock  in  the  material  thrown  back.) 

If  a  trench  is  rammed  or  water-tamped  any  earth  which 
may  have  slipped  or  caved  from  the  bank  shall  be  thrown  out 


208  SEWERAGE. 

of  the  trench  and  the  space  refilled  and  tamped  in  the  same  way 
as  the  trench  proper,  without  extra  compensation.  (Still  another 
plan  is  to  pay  for  rammers  by  force  accounts,  the  engineer  determin- 
ing the  number  to  be  used,  and  reserving  the  right  to  decline  to  use 
any  who  do  not  work  faithfully.} 

Paragraph  28.  Street  Surfaces. —  In  all  paved,  macad- 
amized, or  improved  streets  generally  the  surface  of  the 
trenches  shall  be  finished  without  needless  delay,  in  the  most 
workmanlike  manner,  with  the  same  kind  of  roadway  improve- 
ment that  was  removed  in  excavating  the  trench,  and  so 
that  the  underlying  courses,  as  well  as  the  finished  surface,  shall 
conform  to  the  remainder  of  the  roadway,  and  shall  in  every 
respect  be  equal  in  quality,  character,  materials,  and  workman- 
ship to  the  street  improvement  existing  over  the  line  of  the  trench 
immediately  previous  to  making  the  excavation.  In  restoring 
a  concrete  foundation  that  in  place  shall  be  broken  back  6  inches 
form  the  edge  on  each  side  of  the  excavation  and  cleaned  of  all 
dirt  or  loose  stone  or  cracked  concrete  immediately  before  plac- 
ing the  new  material.  New  concrete  shall  then  be  placed  9 
inches  in  thickness  and  mixed  as  specified  for  sewer  construc- 
tion. New  surface  material,  equal  in  all  respects  to  that  originally 
used,  shall  be  supplied  unless  the  engineer  consider  that  removed 
to  be  suitable  to  be  replaced.  The  restoring  and  maintaining 
of  the  pavement  or  improvement  will  be  paid  for  in  accordance 
with  the  price  bid.  The  area  paid  for  shall  be  a  strip  the  length 
of  the  trench  and  30  inches  wider  than  the  outside  diameter  of 
the  barrel  of  the  sewer  beneath  it. 

Paragraph  29.  Cleaning  up. — As  soon  as  the  trench  has 
been  refilled  and  paving  replaced,  all  stones,  plank,  or  other 
refuse  material  of  whatever  description  deposited  and  left  by 
the  contractor  on  the  streets  shall  be  removed  therefrom  and 
the  said  streets  restored  in  all  respects  to  the  same  condition 
as  before  the  trenching  was  commenced.  All  surplus  earth 
which  may  be  left  on  the  street  after  the  trenches  ha,ve  been 
refilled  as  specified  above  and  which  is  not  desired  and  removed 


SPECIFICATIONS,   CONTRACT,  ESTIMATE  OF  COST.       209 

by  the  city  shall  be  regarded  as  the  property  of  the  contractor, 
and  must  be  removed  as  soon  as  possible  at  his  expense. 

Paragraph  30.  Final  Inspection. — Upon  notification  by 
the  contractor  of  the  completion  of  the  work  herein  contracted 
for  the  engineer  will  carefully  inspect  all  sewers,  appurtenances, 
and  all  other  work  done  by  the  contractor.  In  each 
stretch  of  pipe  sewer  intended  to  be  straight,  light  shall  be 
visible  from  one  end  to  the  other.  Any  broken  or  cracked 
pipes  shall  be  replaced  with  sound  ones,  The  interior  of  brick 
sewers  shall  be  of  the  required  shape  and  dimensions,  sound 
and  of  a  uniform  surface.  Any  deposits  found  in  the  sewers, 
protruding  cement  or  packing,  shall  be  removed  and  the  sewer- 
bore  left  clean  and  free  through  its  entire  length.  There  shall 
be  no  leakage  into  any  stretch  of  sewer  exceeding  that  above 
specified.  All  underdrains  shall  discharge  water  freely  and  give 
evidence  of  having  a  clean  and  open  bore.  All  manholes,  lamp- 
holes,  and  other  appurtenances  shall  be  of  the  specified 
size  and  form  and  of  a  neat  appearance,  and  their  tops  shall 
be  set  to  the  proper  grade.  In  general  the  work  shall  comply 
with  these  specifications,  and  if  found  not  to  do  so  in  any  re- 
spect, shall  be  brought  to  the  proper  condition  by  cleaning, 
pointing,  or,  if  necessary,  excavating  to  and  rebuilding,  all  at 
the  expense  of  the  contractor.  But  if  it  be  found  after 
uncovering  any  pipe  or  other  work  at  the  order  of  the 
engineer  that  no  defect  exists,  or  that  the  defect  was  not  due 
to  any  fault  of  the  contractor,  then  the  expense  of  this  shall 
be  borne  by  the  city. 

ART.  50.     GENERAL  PROVISIONS,  PAYMENTS,  ETC. 

Paragraph  31.  General  Provisions. — If  any  alterations 
in  plan  directed  by  the  engineer  diminish  the  quantity  of 
work  to  be  done  they  shall  not  constitute  a  claim  for  damages 
nor  for  anticipated  profits,  and  any  increase  or  decrease  shall 
be  paid  for  or  deducted  according  to  the  quantity  actually 


210  .      SEWERAGE. 

done,  and  at  the  price  established  for  such  work  under  this  con- 
tract. 

The  contractor  will  be  furnished  with  a  set  of  drawings 
showing  the  details  and  dimensions  necessary  to  carry  out  the 
work,  dimensions  in  figures  thereon  having  precedence  over 
the  scale.  These  plans  and  a  copy  of  these  specifications  are 
to  be  kept  constantly  at  the  work  by  the  contractor  or  his 
authorized  foreman.  The  plans  submitted  to  contractors  for 
proposals  are  to  be  interpreted  in  conjunction  with  the  speci- 
fications, and  descriptions  of  the  character  of  the  work  appear- 
ing on  the  plans  are  made  a  part  of  these  specifications.  No 
deviations  from  the  drawings  will  be  allowed  without  the 
direction  of  the  engineer  to  that  effect. 

Should  it  be  necessary  at  any  time  to  move  monument- 
stones  or  other  permanent  records  the  contractor  shall  not 
disturb  them  until  given  permission  by  the  engineer. 

The  contractor  shall  provide  suitable  stakes,  plank,  and 
forms,  and  render  such  assistance  to  the  engineer,  at  his  own 
expense,  as  may  be  necessary  to  establish  lines  and  grades  for 
the  guidance  of  his  work,  and  shall  carefully  preserve  said  points 
at  all  times. 

The  contractor  shall  take  out,  at  his  own  expense,  all  necessary 
permits  from  the  municipal  or  other  public  authorities,  shall 
give  all  notices  required  by  the  law  or  municipal  ordinances,  and 
shall  pay  all  fees  and  charges  incident  to  the  due  and  lawful 
prosecution  of  the  work  covered  by  this  contract,  and  shall  comply 
with  all  laws  and  regulations. 

Necessary  sanitary  conveniences  for  the  use  of  laborers  in 
the  work,  properly  secluded  from  public  observation,  shall  be 
constructed  and  maintained  by  the  contractor  in  such  manner 
and  at  such  points  as  shall  be  approved  by  the  engineer,  and 
their  use  shall  be  strictly  enforced.  The  collection  in  same  shall 
be  removed  when  and  where  in  the  opinion  of  the  engineer,  it 
is  advisable.  The  contractor  shall  supply  sufficient  drinking 
water  to  all  of  his  employees,  but  only  from  such  sources  as  are 


SPECIFICATIONS,  CONTRACT ,  ESTIMATE  OF   COST.       211 

approved  by  the  engineer.  The  contractor  shall  obey  and  en- 
force such  other  sanitary  regulations  and  orders  and  shall  take 
such  precautions  against  infectious  disease  as  the  local  or  state 
Board  of  Health  may  deem  necessary  and  in  case  of  any  such 
disease  occurring  among  his  employees,  he  shall  arrange  for  the 
immediate  removal  of  the  patient  from  the  work  and  isolation 
from  all  persons  connected  with  the  work. 

If  any  person  employed  by  the  contractor  on  this  work 
shall  appear  to  be  incompetent  or  disorderly  he  shall  be  dis- 
charged immediately  on  the  requisition  of  the  engineer,  and 
such  person  shall  not  again  be  employed  on  the  work. 

Paragraph  32.  Responsibility  for  Injuries. — The  con- 
tractor shall  be  responsible  for  injuries  to  person  and  property 
inflicted  during  the  prosecution  of  the  work,  and  for  all 
damages  caused  by  the  negligence  of  the  contractor  or  any  of 
his  employees,  workmen,  or  servants,  and  the  city  may  at  its 
discretion  withhold  the  amount  of  such  injury  or  damage  from 
any  estimate  due  him  which  may  be  needed  to  make  good 
such  damages  or  injuries,  and  the  city  shall  not  in  any  wise 
be  liable  therefor. 

The  contractor  shall  place  sufficient  lights  on  or  near  the 
work  and  keep  them  burning  from  twilight  to  sunrise,  shall 
erect  suitable  railing  or  protection  about  the  open  trenches, 
and  provide  all  necessary  watchmen  on  the  work  by  day  or 
night,  for  the  safety  of  the  public. 

Paragraph  33.  Imperfect  Work. — When  any  work  or 
material  is  found  to  be  imperfect,  whether  passed  upon  or  not 
by  the  inspector,  the  said  work  shall  be  taken  up  and  replaced 
by  new  work  at  any  time  prior  to  final  acceptance. 

If  the  contractor  shall  be  notified  by  the  engineer  of  any 
requirements  or  precautions  neglected  or  omitted,  or  of  any 
work  improperly  constructed,  he  shall  at  once  remedy  the 
same,  and  if  he  fail  so  to  do  the  engineer,  under  the  direction 
of  the  city,  shall  perform  such  work  at  the  contractor's  expense  and 
deduct  the  same  from  amounts  due  or  to  become  due  the  contractor. 


212  SEWERAGE. 

Paragraph  34.  Unnecessary  Delays. — In  case  of  any 
unnecessary  delay,  in  the  opinion  of  the  engineer,  he  shall 
notify  the  contractor  in  writing  to  that  effect.  If  the  con- 
tractor should  not,  within  5  days  thereafter,  take  such 
measures  as  will,  in  the  judgment  of  the  engineer,  insure  the 
satisfactory  completion  of  the  work  the  engineer  may  then, 
under  authority  from  the  city,  notify  the  aforesaid  contractor 
to  discontinue  all  work  under  this  contract,  and  it  is  hereby 
agreed  that  the  contractor  is  to  immediately  respect  said 
notice  and  stop  work  and  cease  to  have  any  rights  to  posses- 
sion of  the  ground.  The  engineer  shall  thereupon  have  the 
power  to  place  such  and  so  many  persons  as  he  may  deem 
advisable,  by  contract  or  otherwise,  to  work  at  and  complete 
the  work  herein  described,  and  to  use  such  materials  as  he 
shall  find  upon  the  line  of  said  work,  or  to  procure  other 
materials  for  the  completion  of  the  same,  and  to  charge  the 
expense  of  said  labor  and  materials  to  the  aforesaid  contrac- 
tor; and  the  expense  so  charged  shall  be  deducted  and  paid 
by  the  party  of  the  first  part  out  of  such  money  as  may  be 
then  due,  or  at  any  time  thereafter  become  due,  to  said  con- 
tractor under  and  by  virtue  of  this  agreement  or  any  part 
thereof;  and  in  case  such  expense  is  less  than  the  sum  which 
would  have  been  payable  under  this  contract  if  the  same  had 
been  completed  by  the  party  of  the  second  part  [he]  [they] 
shall  be  entitled  to  receive  the  difference,  and  in  case  such 
expense  is  greater  the  party  of  the  second  part  shall  pay  the 
amount  of  such  excess  so  due. 

Paragraph  35.  Extra  Work. — If  any  work  of  the  general 
nature  of  the  work  herein  contracted  for,  but  for  doing  which 
a  bid  has  not  been  especially  made,  shall  need  to  be  done  the 
contractor  shall  do  the  same  under  the  direction  of  the 
engineer,  and  shall  receive  therefor  the  actual  cost  of  labor 
and  material  used  plus  ten  per  cent  (io#)  for  superintendence 
and  use  of  tools,  but  he  shall  not  be  entitled  to  receive  pay- 
ment for  any  work  as  extra  work  unless  ordered  by  the 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.         213 

engineer  to  do  the  same  as  such.  No  claim  for  extra  work 
will  be  allowed  if  not  made  before  the  payment  of  the  next 
following  monthly  estimate. 

Paragraph  36.  Time  of  Commencement  and  Completion. 
— The  party  of  the  second  part  agrees  to  begin  the  work 
herein  contracted  for  within  two  weeks  of  the  awarding  of  the 
contract,  and  to  fully  complete  the  work  herein  specified  on 

or  before  the day  after  the  awarding  of  said  contract; 

but  the  party  of  the  first  part  may  extend  the  time  of  com- 
pletion should  they  deem  it  for  the  best  interest  of  the  city. 
[It  is  expressly  understood  that  the  party  of  the  second  part 
agrees  to  pay  all  expenses,  such  as  engineering  and  inspec- 
tion, that  the  city  may  be  put  to  by  reason  of  the  work  being 
incompleted  at  the  time  specified  in  the  contract.]  [For  each 
day  after  the  time  specified  that  the  contract  remains  un- 
completed $25  will  be  deducted  from  the  amount  due  the 
contractor,  and  for  each  day  by  which  the  contract  is  com- 
pleted previous  to  the  time  specified  the  contractor  shall  be 
entitled  to  a  bonus  of  $25.]  [For  each  day  after  the  time 
specified  that  the  contract  remains  uncompleted  $25  will 
be  deducted  from  the  amount  due  the  contractor,  and  it 
is  hereby  expressly  understood  that  said  sum  shall  be  deemed 
and  taken  in  all  courts  to  be  the  liquidated  damages  for  the 
non-performance  of  the  work  in  the  manner  aforesaid,  and  not 
in  the  nature  of  a  penalty.] 

Paragraph  37.  Definitions. — Whenever  the  word  "  en- 
gineer "  is  used  in  the  specifications  it  refers  to  the  engineer 
in  charge  of  the  work  and  also  to  his  authorized  agents. 

The  "  party  of  the  first  part  "  is  the  city  by  and  for  which 
the  work  herein  described  and  referred  to  is  being  done,  and 
the  "  party  of  the  second  part  "  is  the  person  or  persons  con- 
tracting to  do  said  work. 

The  word  "  sewer  "  in  its  general  sense  in  these  specifica- 
tions refers  to  the  sewer-barrel  and  to  any  bends,  slants, 
branches,  or  other  details  joined  to  or  forming  a  part  thereof. 


214  SEWERAGE. 

The  word  "  appurtenance  "  refers'  to  all  manholes,  lamp- 
holes,  flush-tanks,  inlets,  and  all  structures  forming  a  part  of 
the  sewerage  system,  but  not  included  in  the  term  "  sewer." 

Paragraph  38.  Position  of  the  Engineer. — The  engineer 
sliall  have  the  final  decision  on  all  matters  of  dispute  involving 
the  character  of  the  work,  the  compensation  to  be  made 
therefor,  or  any  question  arising  under  this  contract.  He 
shall,  as  representing  the  city,  have  the  option  of  making  any 
changes  in  the  line,  grade,  plan,  form,  position,  dimensions, 
or  material  of  the  work  herein  contemplated,  either  before  or 
after  construction  is  begun,  and  all  explanations  or  directions 
necessary  for  carrying  out  and  completing  satisfactorily  the 
different  descriptions  of  work  contemplated  and  provided  for 
under  this  contract  will  be  given  by  said  engineer. 

Paragraph  39.  Duties  of  the  Contractor. — The  contrac- 
tor must  perform  the  work  contracted  for  strictly  according  to 
these  specifications,  and  follow  at  all  times,  without  delay,  all 
orders  and  instructions  of  the  engineer  in  the  prosecution  and 
completion  of  the  work  and  every  part  thereof,  and  constantly 
be  on  the  ground  or  be  represented  by  a  duly  qualified  person 
to  look  after  the  work  and  receive  instructions. 

Paragraph  40.  Measurements  and  Payments. — Meas- 
urements of  sewers  and  drains  shall  be  taken  from  the  centre 
of  the  uppermost  manhole  or  flush-tank  on  each  line  to  the 
centre  of  the  manhole  at  its  junction  with  a  main  or  lateral, 
or  to  the  centre  line  of  such  main  or  lateral  at  the  junction, 
including  all  branches,  manholes,  or  other  appurtenances 
along  the  line;  said  measurement  being  taken  parallel  to  the 
axis  of  the  sewer  barrel.  The  depth  by  which  sewer  prices  will  be 
graded  will  be  measured  from  the  surface  of  the  ground  to  the 
under  side  of  the  sewer-pipe  or  masonry  or  of  the  timber 
platforms  or  foundation-sills.  The  price  bid  for  sewers  or 
drains  shall  include  furnishing  all  material  and  labor  for 
excavating,  shoring,  constructing  the  sewer  or  drain  in 
accordance  with  the  specifications  and  plans,  back-filling, 


SPECIFICATIONS,  CONTRACT,  ESTIMATE   OF  COST.      215 

restoring  the  street-surface  as  previously  specified,  and  for  all 
matters  in  connection  therewith  heretofore  specified  as  being 
so  included.  Measurements  of  connections  shall  be  taken 
from  the  outside  (bell)  end  of  the  branch  to  the  upper  end  of 
the  connection-pipe.  Branches  shall  be  paid  for  by  the  piece 
at  the  price  bid,  which  shall  include  the  cost  of  furnishing  and 
fixing  plugs  in  said  branches  where  necessary. 

Deep-cut  connections  shall  be  paid  for  at  the  prices  bid 
for  "  deep-cut  connections,"  "  pipe,"  "  concrete,"  and 
"  timber  in  foundations,"  according  to  the  actual  quantities 
used,  the  bid  for  "deep-cut  connections"  including  the 
combining  of  these  and  the  setting  of,,  and  extra  care  in  back- 
filling around,  the  pipe. 

Flush-tanks  shall  be  paid  for  at  the  price  bid  for  each  par- 
ticular size  of  tank,  this  to  include  the  tank  complete  as  set 
forth  in  the  drawings  and  specifications,  including  the  excava- 
tion and  back-filling,  ventilation-pipe  and  iron  head. 

Ordinary  manholes  and  lamp-holes  shall  be  paid  for  on  the 
basis  of  a  depth  of  8  feet,  with  an  additional  amount  for  each 
foot  by  which  the  depth  exceeds  8  feet,  the  price  bid  to 
include  excavating  and  back-filling,  furnishing  and  setting  iron 
castings  and  steps,  and  completing  the  whole  as  set  forth  in 
the  plans  and  specifications.  The  depth  of  flush-tanks,  man- 
holes, and  lamp-holes  shall  be  measured  from  the  invert  of  a 
pipe  sewer,  or  the  springing  of  a  brick  or  concrete  sewer,  to  the 
top  of  the  iron  head  when  properly  set. 

The  price  bid  for"  crossing-"  and  "  drop-manholes  "  shall 
be  an  additional  sum  over  and  above  the  bid  for  the  same  as 
a  regular  manhole,  and  shall  be  held  to  cover  furnishing 
material  for  and  constructing  the  crossing  or  drop  device  as 
shown  in  the  plans,  as  an  addition  to  the  regular  manhole. 
The  bid  for  the  crossing-manhole  shall  be  a  lump  sum;  that 
for  the  drop-manhole  shall  be  per  vertical  foot,  measuring 
from  the  invert  of  the  lower  to  that  of  the  upper  sewer. 


2i6  SEWERAGE. 

The  price  bid  for  inlets,  catch-basins,  and  other  appurte- 
nances shall  include  the  excavation  and  back-filling,  and  fur- 
nishing all  materials  and  constructing  each  appurtenance  in 
strict  conformity  to  the  plans  and  specifications. 

The  price  bid  for  stone  paving  shall  be  per  square  foot, 
and  shall  be  over  and  above  the  price  for  the  sewer  or  man- 
hole in  which  it  is  laid. 

The  price  for  stone,  brick,  or  concrete  masonry  not  other- 
wise provided  for  shall  be  per  cubic  yard  by  actual  measure- 
ment in  place,  provided  such  dimensions  do  not  exceed  those 
indicated  or  implied  in  the  plans  or  instructions  of  the  engineer. 

Iron-work,  both  cast  and  wrought,  shall  be  paid  for  by  the 
pound,  but  no  payment  for  iron-work  as  such  shall  be  made 
for  the  heads  or  steps  or  other  devices  included  in  the  man- 
holes and  other  appurtenances  as  shown  in  the  plans  and  speci- 
fications. Cast-iron  pipe  will  be  paid  for  at  the  price  per  foot 
bid  for  the  same. 

The  price  for  timber  in  foundations  shall  include  the  fur- 
nishing and  setting  of  the  same.  The  price  bid  for  furnishing 
piles  shall  be  for  the  lengths  actually  delivered,  where  these 
do  not  exceed  those  ordered  by  the  engineer.  The  price  for 
driving  piles  shall  be  per  foot,  measured  from  the  bottom  of 
the  pile  when  driven  to  the  surface  of  the  ground  in  which  it 
is  driven,  and  shall  include  cutting  off  the  piles  at  the  eleva- 
tion given  by  the  engineer. 

The  price  bid  for  tamping  trenches  shall  be  by  the  cubic 
yard  of  trench  above  a  point  2  feet  above  the  top  of  the 
sewer,  the  bottom  width  heretofore  specified  being  allowed 
and  side  slopes  of  I  in  15  in  earth  and  I  in  8  in  rock. 

The  price  bid  for  repaving  shall  include  the  necessary  grading 
and  tamping  of  the  top  surface  of  the  trench,  and  replacing  the 
pavement  as  specified,  including  furnishing  such  new  material 
as  may  be  required;  also  maintaining  the  pavement  for  one  year 
after  the  completion  of  this  contract. 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF  COST.       217 

The  engineer  on  the  first  of  each  month,  or  within  5  days 
thereafter,  during  construction,  will  estimate  approximately 
the  amount  of  work  completed  during  the  preceding  month, 
according  to  these  specifications,  and  eighty-five  per  cent 
(85$)  of  the  amount  due  beyond  the  reservations  herein  made 
will  be  paid  the  contractor  on  or  before  the  I5th  day  of  each 
month  for  the  work  of  the  preceding  month. 

When  the  contract  shall  have  been  completely  performed 
on  the  part  of  the  contractor  the  engineer  shall  proceed  to 
make  final  measurements  and  estimates  of  the  same,  and  shall 

certify  the  same  to  the  city ,  who  shall,  except  for 

cause  herein  specified,  pay  to  the  contractor,  on  or  before  the 
1 5th  day  after  such  completion  of  the  contract,  the  balance 
which  shall  be  found  due,  excepting  therefrom  such  sum  as 
may  be  lawfully  retained  under  any  provision  of  this  contract. 

ART.  51.     CONTRACT. 

Accompanying  the  specifications  and  bound  with  them  should 
be  the  contract  proper,  of  which  a  form  is  given  : 

THIS  AGREEMENT,   made   and  concluded  the 

day  of in  the  year  One  Thousand  Nine  Hundred 

and ,  by  and  between  the  City  of , 

of   the  first    part,  and ,  Contractor,  of  the 

second  part, 

WlTNESSETH,  That  the  said  party  of  the  second  part  (has) 
(have)  agreed,  and  by  these  presents  (does)  (do)  agree  with 
the  said  party  of  the  first  part,  for  the  considerations  herein 
mentioned  and  contained,  and  under  the  penalty  expressed 
in  a  bond  bearing  even  date  with  these  presents  and  hereto 
attached,  to  furnish  at  (his)  (their)  own  proper  cost  and 
expense  all  the  necessary  material  and  labor,  except  as  herein 
specially  provided,  and  to  excavate  for  and  build,  in  a  good, 
firm,  and  substantial  manner,  the  sewers  indicated  on  the 


2l8  SEWERAGE. 

plans  now  on  file  in  the  office  of  the  city  engineer,  and  the 
connections  and  appurtenances  of  every  kind  complete,  of  the 
dimensions,  in  the  manner,  and  under  the  conditions  herein 
specified ;  and  (has)  (have)  further  agreed  that  the  engineer  in 
charge  of  the  work  shall  be  and  is  hereby  authorized  to 
inspect  or  cause  to  be  inspected  the  materials  to  be  furnished 
and  the  work  to  be  done  under  this  agreement,  and  to  see 
that  the  same  correspond  with  the  specifications. 

The  party  of  the  second  part  hereby  further  agrees  that 
(he)  (they)  will  furnish  the  city  with  satisfactory  evidence  that 
all  persons  who  have  done  work  or  furnished  material  under 
this  agreement,  and  are  entitled  to  a  lien  therefor  under  any 

law  of  the  State  of ,  have  been  fully  paid  or  are 

no  longer  entitled  to  such  lien,  and  in  case  such  evidence  be 
not  furnished  as  aforesaid  such  amount  as  the  party  of  the 
iirst  part  may  consider  necessary  to  meet  the  lawful  claims  of 
the  persons  aforesaid  shall  be  retained  from  the  moneys  due 
the  said  party  of  the  second  part,  under  this  agreement,  until 
the  liabilities  aforesaid  may  be  fully  discharged  and  the  evi- 
dence thereof  furnished. 

The  said  party  of  the  second  part  further  agrees  that  (he) 
(they)  will  execute  a  bond  in  a  sum  equal  to  25  per  cent  of 
the  contract  price,  secured  by  a  responsible  Indemnity  or 
Guarantee  Company  of,  or  authorized  by  law  to  do  business 

in,  the  State  of and  satisfactory  to  the  city,  or  by 

at  least  three  responsible  freeholders  of County 

satisfactory  to  the  city,  for  the  faithful  performance  of  this 
contract,  conditioned  to  indemnify  and  save  harmless  the  said 
city,  its  officers  or  agents,  from  all  suits  or  actions  of  every 
name  or  description  brought  against  any  of  them  for  or  on 
account  of  any  injuries  or  damages  received  or  sustained  by 
any  party  or  parties,  by  or  from  the  said  party  of  the  second 
part,  (his)  (their)  servants  or  agents,  in  the  construction  of 
said  work,  or  by  or  in  consequence  of  any  negligence  in  guard- 
ing the  same  or  any  improper  materials  used  in  its  construe- 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.      2ig 

tion,  or  by  or  on  account  of  any  act  or  omission  of  the  said 
party  of  the  second  part,  or  (his)  (their)  agents,  in  the  per- 
formance of  this  agreement  and  for  the  faithful  performance 
of  this  contract  in  all  respects  by  the  party  of  the  second  part; 
and  the  said  party  of  the  second  part  hereby  further  agrees 
that  so  much  of  the  moneys  due  to  (him)  (them),  under  and 
by  virtue  of  this  agreement,  as  shall  be  considered  necessary 
by  the  said  city  may  be  retained  by  the  said  party  of  the  first 
part,  until  all  such  suits  or  claims  for  damages  as  aforesaid 
shall  have  been  settled  and  evidence  to  that  effect  furnished 
to  the  satisfaction  of  said  city. 

The  said  party  of  the  first  part  hereby  agrees  to  pay, 
and  the  said  party  of  the  second  part  agrees  to  receive, 
the  following  prices  as  full  compensation  tor  furnishing  all 
materials,  labor,  and  tools  used  in  building  and  constructing, 
excavating  and  back-filling,  and  in  all  respects  completing  the 
aforesaid  work  and  appurtenances,  in  the  manner  and  under 
the  conditions  before  specified,  and  as  full  compensation  for 
all  loss  or  damages  arising  out  of  the  nature  of  the  work  afore- 
said, or  from  the  action  of  the  elements  or  from  any  unfore- 
seen obstructions  or  difficulties  which  may  be  encountered  in 
the  prosecution  of  the  same,  and  for  all  expenses  incurred  by 
or  in  consequence  of  the  suspension  or  discontinuance  of  the 
said  work,  and  for  well  and  faithfully  completing  the  same  and 
the  whole  thereof  according  to  the  specifications  and  require- 
ments of  the  engineer  under  them,  to  wit: 

(Insert  here  spaces  for  making  bids,  being  careful  to  include 
every  item  for  which  bids  are  invited.     As  an  example:} 

For  all  36-inch  brick  sewer,  trenches 

from  6  to  8  feet  deep. $ per  lineal  foot 

For  water-tamping per  cubic  yard 

For  each  manhole  8  feet  deep,  complete 

For  each  vertical  foot  of  manhole  more 

than  8  feet  deep,  8-inch  wall 


220  SEWERAGE. 

For  each  vertical  foot  of  manhole  more 

than  8  feet  deep,  12-inch  wall 

For  timber  foundations per  M  B.  M. 

etc.     etc. 

» 

IN  WITNESS  WHEREOF  the  said  party  of  the  second  part 
(has)  (have)  hereunto  set  (his)  (their)  hand  and  seal  and  the 
said  party  of  the  first  part  has  caused  these  presents  to  be 

sealed  with  its  common  seal  and  to  be  signed  by  the 

on  the  day  and  year  above  written. 


It  is  recommended  that  the  engineer  refer  to  Johnson's 
"  Contracts  and  Specifications,"  and  Wait's  "  Law  of  Contracts," 
where  will  be  found  a  full  discussion  of  the  subject  from  both  the 
legal  and  engineering  standpoint. 

ART.  52.  ESTIMATE  OF  COST. 

It  is  generally  desirable,  and  frequently  required  by  law,  that 
a  careful  estimate  be  made  of  the  cost  of  the  work  to  be  done. 
For  this  purpose  map,  plans,  specifications,  and  profile  should 
be  carefully  studied  to  obtain  quantities,  and  the  amount  of 
rock  to  be  excavated,  and  locations  of  quicksand  and  ground-water 
ascertained,  and  in  general  as  careful  a  study  made  of  the 
conditions  as  a  contractor  would  make  before  bidding.  Also 
the  prices  of  materials  should  be  obtained,  including  the  cost 
of  getting  them  upon  the  ground,  and  from  these  as  close  an 
estimate  made  as  possible  of  the  actual  cost  of  constructing 
the  system.  To  this  should  be  added  10  to  100  per  cent  for 
profit  and  contingencies,  the  latter  amount  when  the  work  is 
to  be  done  under  great  risks  and  subject  to  possible  losses. 

Out  of  a  dozen  bids  made  on  one  sewer  contract  there  are 
generally  one  or  two  quite  low,  two  or  three  others  quite  high, 
and  the  remainder  more  or  less  close  together  midway  between 
these,  and  usually  representing  a  fair  price  for  the  work,  which 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF    COST.       221 

also  the  engineer's  estimate  should  do.  The  estimate  should 
not  be  too  low,  as  this  often  gives  rise  to  suspicion  of  intentional 
deception  of  the  city,  and  if  made  the  basis  of  an  appropriation  of 
funds  for  construction  may  lead  to  a  forced  curtailment  of  the 
amount  of  work  done.  On  the  other  hand,  an  unduly  high 
estimate  may  discourage  any  appropriation  whatever.  Prob- 
ably no  act  of  the  sewerage  engineer  is  more  readily  appre- 
ciated by  the  public  at  large  than  the  making  of  an  estimate 
closely  approximating  the  actual  cost. 

The  cost  of  brick,  lumber,  and  sand  varies  with  each 
locality  and  should  be  obtained  from  local  dealers.  That  of 
cement  and  pipe  varies  little  except  with  the  freight,  and  this 
variation  is  slight  between  different  places  in  the  same  section 
and  on  main  freight-lines. 

A  schedule  price  has  been  adopted  by  all  sewer-pipe  makers 
east  of  the  Mississippi,  and  another  by  those  west  of  the  Mis- 
sissippi, from  which  large  discounts  are  allowed.  The  list  prices 
of  the  eastern  manufacturers  are  given  en  page  222. 

Slants  are  charged  50  per  cent  more  than  plain  pipe,  and 
measured  on  the  long  side  of  the  slant,  but  none  less  than  12 
inches  long. 

Double-strength  pipe  is  generally  allowed  10  per  cent  less 
discount  than  standard  pipe. 

Increasers  are  pipe  with  the  hub  on  the  small  end  and 
reducers  with  the  hub  on  the  large  end,  and  are  charged 
double  the  price  of  2  feet  of  pipe  of  the  size  of  the  large  end. 

Channel  or  split  pipe,  which  is  pipe  cut  in  two  or  more 
pieces  lengthwise,  costs  |  the  price  of  whole  pipe. 

Stoppers  or  plugs  for  closing  pipe  cost  £  as  much  as  I  foot 
of  pipe  of  the  size  in  which  they  are  used. 

TABLE  No.  18. 

LIST    PRICES    OF    DRAIN-TILE. 


Size    inches  

2 

2* 

d       1       * 

6     1     8 

10 

12 

Price,  straight  pipe  

.012 

.015 

.O2O 

4             5 
.030      .040 

•055  1  .080 

.140 

.200 

222 


SEWERAGE. 


£  s 


a  § 


Annular 
Space. 

a    *  7 

O  —  '    ij 

Prt12         J 

o  PL, 
'|o 

-^  3 

H     OH 

Io 

•§  g 

.|*0 

B'fl 

*3    ® 

H-  > 

W2 

Depth  of 
Socket. 

O-     :  . 

;  !  inn:  i7_^,  j  !  j  1 

h  ' 

H«H^«^^              HOOH^HC^'*              H^ 

Weight 
per  Foot. 

£43 

0  *->                         „: 

1|      3 

|l       2 

MHMp<(Nf0TOOOOMTroTO^ 

"8 

h 

f 

".e 

o.|               J 

•;••'•*;• 

11      I 

w 

*«—  -*-Mrrr«r.r!rs 

V 

Branches. 

if*!  i 

:  :       :  :  :  :    at??&?E?R 

•     •               ....       oo  d  O  «^  ^O  <*500  00  r^ 
•     •                                       M   N  ro  PO  •*  "TO  r^oo 

00        a        00 

2  i-  9-5  W  c;S  c-g 

^J^'gRR^gg^^S^SR 

rSf^^|5|2H 

-HMNN"^a-S""-^- 

|Sg^gIs  -g 

WWOOOOOOOOOOOO     ^     ]     [     ] 

fe  M^j  ^  w  M          ^j 
<N"                  "  O 

i/^oo   O  f»  "100  "^00  O 
•     •  00  00  t-  O  -too  w  00  10 

1 

jjwsmMssswarii 

The  above  prices  and  dimensio 
of  the  western  manufacturers  are  sli 

fe  bfl^^^^  g     43 

^  °  °  M                  M  H  H  i  !     ; 

ll|      1 

OOvntoOOOOOOOOOOOOOO 
10  CriO  00  «   0  •*  0  O   'TOO   0  O   O  O  "1  O  «o 

f/>                                                                                w    M    M    N    (^  <*} 

rfS 

^s^a^o-sRSie^asg 

OOOOOOOOii'-tMNNfO'*'  "^O  r^ 

ill 

N    W>  T  «OO  00    Ov  O    M   >r'OO    O    M    •*  «^  O    "5O 

SPECIFICATIONS,  CONTRACT,  ESTIMATE   OF  COST.       223 

36-  and  38-inch  WOODEN-STAVE  PIPE  in  Los  Angeles, 
Cal.,  cost  $2.25  to  $2.50  per  foot,  complete.* 

Light-weight  CAST-IRON  PIPE,  first  quality,  cost  in  1910 
about  as  follows: 

TABLE  No.  19. 

COST    OF    LIGHT    IRON    PIPE. 


Size,  inches.  .  . 
Cost  per  foot.. 

4 

•3° 

6 

.40 

8 
-52 

10 

•77 

12  1  14 
.96|i.io 

16 
1.30 

18 
1.50 

20 

2.OO 

22 
2.25 

24 

2-75 

27  j  30 

3-iol3-75 

33 
4-15 

One  barrel  of  cement,  used  neat,  should  lay  the  following 
lengths  of  sewer,  pipes  3  feet  long: 

TABLE  No.  20. 

LENGTHS    OF    PIPE    SEWER    ONE    BARREL    OF    CEMENT    WILL    LAY. 


Size,  inches... 
Length,  feet  .. 

4 
500 

6 
350 

8     9 

200  1  175 

IO 

150 

12 
100 

15 

75 

18 
65 

20 

60 

24 

50 

The  following  gives  approximately  the  lowest  practicable 
cost  of  excavating  trenches  in  compact  loam  or  material 
excavated  with  equal  ease.  The  prices  for  shoring  and 
sheathing  are  to  be  added  where  necessary.  These  are  based 
on  continuous  work  with  gangs  of  the  most  economical  size. 
House -connections  or  other  short  lines  would  cost  more. 
Profit  is  not  included.  Trench  machines  excavate  at  a  cost 
of  12  to  1 8  cents  per  cu.  yd.,  plus  $175  to  $400  per  month 
rental. 


*  See  also  "  Water-supply  Engineering,"  p.  448. 


224 


SEWERAGE. 


TABLE  No.  21. 

COST   OF   EXCAVATING  AND   BACK-FILLING  AND   OF   SHEATHING; 
DOLLARS   PER   LINEAL   FOOT. 

(Compact  loam;    no  ground-water;    no  machinery.     Most  favorable  average 

conditions.) 


Depth  of  trench   feet 

•g 

g 

18 

4-  to  xo-inch  sewer 

j  j 

j  r 

21 

TO 

60 

QQ 

it-inch  sewer 

1  3 

18 

26 

•3« 

36 

•o  1 

ou 
60 

7  C 

20    "         " 

i? 

22 

?  2 

d.4. 

c  7 

7O 

•  /3 

88 

24    "        '  '     

18 

26 

36 

CQ 

67 

go 

I    OO 

I    7  < 

30    "        "    . 

21 

?o 

d.2 

<;8 

7^ 

QO 

I    I  tj 

1  -JJ 

I     ^O 

Close             f  Lumber,  @  $15.. 
sheathing  \  Setting 

•51 
12 

.63 

I  A 

•$ 

.96 
20 

1.20 
•20 

1.38 
•j  -i 

1.  60 

16 

A  -O*-7 

1.83 

If  used  2i  times* 

•5-1 

•2Q 

d8 

<7 

•Ow 

7  < 

"87 

•»5U 
I    OO 

•oy 
i  i  ^ 

Skeleton  sheathing-planks  4  feet 
apart  .... 

ir 

18 

22 

27 

^6 

40 

Af 

1  •  AD 

<o 

*  Three-fourths  used  the  second  time,  one-half  the  third  time,  one-fourth  the  fourth 
time.  With  care  8°od  sheathing  may  be  used  an  average  of  three  to  five  times  where 
driving  is  easy. 

QUICKSAND  may  cost  from  two  to  ten  times  the  above.  No 
estimate  can  be  given  for  it.  ROCK  EXCAVATION  in  sewer- 
trenches  usually  costs  from  75  cents  to  $2  per  cubic  yard. 
The  greater  the  amount  of  rock  per  running  foot  to  be 
excavated  the  more  cheaply  it  can  be  done. 

The  approximate  cost  of  laying  sewer-pipe,  including  all 
but  the  excavation,  is  given  in  the  following  table: 


TABLE  No.  22. 

COST   OF   LAYING  SEWER-PIPE,    CENTS   PER   LINEAL   FOOT. 


2-foot 

Lengths. 

3  -foot  Lengths. 

4 

0.7 

i.S 
0.6 

2.8 

5 

0.8 

i.S 
0.7 

3-0 

6 
i  .0 

y 

3.3 

8 

i-S 

1.6 
0.8 

3-9 

9 

1-7 

1.8 
0.9 

4-4 

10 

2  .  O 

2  .0 
I  .  O 

5-0 

12 

2-5 
2-5 

i-3 
6-3 

IS 

3-5 

3-° 
i  .6 

8.1 

18 

4-5 

3-5 
1-9 

9-9 

20 

5-5 
4.0 

2  .  2 

24 
7.0 

4-7 
2-9 

27 

9.0 

5-5 
3-4 

30 

II.  O 

6.0 
4.1 

36 

iS-o 

8.0 
6.6 

29.6 

Unloading,     hauling,     and 
distributing  *  
Laying,    cost  of  jute  and 

Cement,  mixed  
Total        

II-7 

14.6 

17.9 

21  .  I 

*  Teams  hauling  2500  to  3000  pounds  per  load;   average  haul  one  mile;   $3.50  per  day. 


SPECIFICATIONS,   CONTRACT,  ESTIMATE  OF  COST.       225 


The  approximate  cost  of  building  circular  brick  sewers  is 
given  in  the  following  table.  This  does  not  include  excavation 
or  back-filling. 

TABLE  No.  23. 

COST   OF   CIRCULAR   BRICK  SEWERS   PER    LINEAL  FOOT. 

(Material  and  mason  work  only.) 


Interior  Diameter,  Feet. 

One  Ring. 

Two  Rings. 

Three  Rings. 

2 

3 

3 

4 

5 

5 

6 

Brick  @  $10  per  M                         ... 

•5° 
.11 

-03 
.16 

-15 

-73 
.16 
.04 

.22 
.22 

1.64 

-35 
.08 
.48 
-45 

2.14 

-44 
.10 
.60 
-58 

2.63 

-54 
-14 
.72 
.70 

4.20 

-87 
.22 

*-*5 

I.  08 

4-94 
1.05 
.26 
i-47 
J-43 

Mixed  /  Cement,  @  $1.20  per  bbl.  .  .  . 
i*  2    "1  Sand  @/  $i  oo  per  yd  

Masons  @  $4  oo  per  day     

Helpers  @  $i  50  "     "   

Total       

-95 

1-37 

3.00 

3-86 

4-73 

7-52 

9-iS 

CONCRETE   SEWERS,   if  designed   according   to   the  formula 
=  i-\ (all  dimensions  in  inches)   will  require  a  theoretical 


12 


amount  of  concrete  represented  by  the  formula, 
Q  =  0.007295^  +0.09427^  +0.0808, 

in  which  Q  is  the  cubic  yards  of  concrete  required  for  100  feet  of 
sewer,  and  d  is  the  inside  diameter,  in  inches.  From  5  to  10 
per  cent  should  be  added  for  waste,  expanding  of  forms,  etc. 
In  estimating  cost  be  sure  to  allow  sufficient  for  setting  up  and 
taking  down  forms.  Where  collapsible  sheet  steel  forms  are 
used  this  cost  is  about  5  to  10  cents  per  lineal  foot  for  diameters 
up  to  5  feet. 

The  approximate  cost  of  manholes,  3  feet  by  4  feet  6  inches 
on  the  bottom,  is  given  in  the  following  table.  A  4-foot  circular 
manhole  will  cost  about  4  per  cent  more.  This  table  does  not 
include  the  cost  of  excavation,  foundation  or  of  the  iron-work. 


226 


SEWERAGE. 


The  brickwork  is  taken  as  8  inces  thick  down  to  a  depth  of  12 
feet,  and  below  this  as  12  inches  thick. 

TABLE  No.  24. 

COST    OF    MANHOLES,    3    FT.  X  4    FT.    6    IN. 

(Brick  2  in.X4  in.XS  in.:  J-inch  joints.) 


Depth,  Top  of  Brickwork  to  Sewer- 
invert. 

8ft. 

i  oft. 

12  ft. 

1  4  ft. 

1  6  ft. 

i8ft. 

20  ft. 

Brick   @  $10  per  M 

$ 
12    0^ 

$ 

i*  88 

$ 

18  80 

$ 
2^    7^ 

$ 

2O      O6 

$ 

27  .AC 

$ 
37    7O 

Mixed  /  Cement,  @  $1.20  per  bbl..  .  . 
i  '  ^    1  Sand   $i  oo  per  yd. 

1.48 
^2 

1.82 
65 

2-15 
,7q 

2.72 

.QC 

3-32 
I.  1C 

3-82 

I.7C 

4-31 

I  .  ^O 

I^lasons   @  $4  oo  per  day  

T.    2O 

1      7O 

4-2^ 

c.2t; 

6.25 

7.2i; 

8.25 

Helpers  @  $i  50  per  day  

2    40 

2.80 

T,  .20 

-2  .QC 

4.70 

5-45 

.      J 

6.20 

Total 

20  ?t; 

24.   SE? 

2O    I  C 

36  62 

44  48 

^i  .  32 

^7.06 

Foundation  of  concrete  6  inches  thick,  with  benches  for  8-inch  pipe . .   $5 .00 

Cast-iron  tops  and  covers,  450  to  800  pounds,  @  2  cts $9.00-$! 6.00 

Steps,  wrought  iron,  each 25  cts. 

In  the  above  tables  labor  is  taken  at  $1.50  per  day,  teams 
at  $3.50.  The  cost  given  does  not  include  superintendence, 
use  of  tools,  profit,  or  any  of  the  general  expenses  of  manage- 
ment, but  is  thought  to  be  liberal,  and  sufficient  to  include 
these  under  good  management. 

Natural  CEMENT  can  be  had  in  the  Eastern  States  at  from 
65  cents  up,  Portland  from  $1.20  up,  per  barrel  in  car-load  lots. 

The  cost  of  SAND  will  vary  with  the  locality  from  25  cents 
to  $2  per  cubic  yard. 


ART.  53.     METHODS  OF  ASSESSMENT. 

While  not  an  engineering  feature  of  sewer  construction, 
the  methods  employed  in  paying  for  a  system  may  be  briefly 
considered  to  advantage.  In  many  cases  the  city  pays  for 
the  construction  and  later  reimburses  itself  by  special  assess- 
ments on  benefited  property  or  by  annual  rental;  in  some 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF   COST.        227 

the  entire  cost  is  borne  by  the  city  at  large;  in  others  part  is 
borne  by  the  city,  part  by  the  property-owners.  The  city's 
payment  may  be  made  from  the  ordinary  funds  or  by  issuing 
sewerage  bonds.  In  a  few  large  cities  the  assessment  bills  are 
assigned  to  the  contractor,  with  right  of  lien  for  collection. 

"  In  a  majority  of  cases  the  city  pays  for  main  sewers, 
either  wholly  or  all  above  the  usual  assessment  for  a  branch 
sewer.  A  large  number  also  assess  this  expense  by  the  area 
method  upon  the  property  affected,  either  entirely  or  all 
exceeding  the  usual  charge  for  a  lateral,  as  before.  Less 
commonly  a  percentage  is  assessed  and  the  city  pays  the 
balance,  or  the  cost  is  divided  between  an  area  and  a  frontage 
charge,  or  other  plans  are  followed  in  its  distribution.  Of  the 
methods  pursued  in  providing  for  the  collecting  system,  con- 
sisting of  the  laterals  or  branch  sewers,  a  plurality  prefer  to 
charge  the  cost  upon  abutting  property  according  to  the 
frontage  rule;  though  nearly  an  equal  number  have  an  arbi- 
trary rate  per  foot  front,  varying  from  30  cents  to  $2,  the  city 
to  pay  the  balance;  and  a  considerable  number  assess  the  cost 
either  upon  the  drainage-district  or  upon  a  zone  of  a  certain 
width  on  each  side  of  the  sewer,  in  the  ratio  that  the  area  of 
the  lot  or  land  in  question  bears  to  the  total  assessed  area, 
streets  being  excluded.  Of  the  remaining  methods  some 
divide  the  expense  between  the  city  and  private  property  by 
various  processes,  others  charge  it  upon  property  by  a  com- 
bination of  the  frontage  and  area  rules,  and  sometimes  the 
city  bears  the  whole  cost. 

"  The  frequently  occurring  plan  of  assessing  upon  contigu- 
ous property  the  equivalent  expense  of  a  sewer  of  small  size, 
where  a  large  sewer  is  placed,  is  commendable.  This  method 
would  obviously  have  no  advantage  where  the  total  cost  of 
both  mains  and  branches  are  together  distributed  pro  rata 
upon  all  the  property  benefited,  nor  any  application  where 
the  city  pays  entirely  for  its  sewer  system ;  but  where 


228  SEWERAGE. 

adjacent  property  is  charged  with  a  certain  part  or  all  the 
expense  of  the  sewer,  inequality  would  result  if  the  method 
just  indicated,  or  an  equivalent  specified  fixed  charge  not 
depending  on  the  size  of  pipe,  is  not  applied.  Necessarily 
the  larger  sewers  are  laid  on  the  lower  ground,  where,  except 
manufactoiies  and  similar  industries,  the  less  valuable  and 
productive  property  occurs.  Here,  also,  are  more  generally 
found  tenements  and  the  habitations  of  laboring  men  who  are 
less  able  to  meet  the  burden,  while  the  commercial  districts, 
and  especially  the  dwellings  of  the  more  prosperous,  are  in 
the  higher  portions  of  the  city,  where  the  sewers  are  naturally 
of  smaller  size.  The  latter  classes  of  citizens  make  the  greater 
use  of  sewers,  and  it  would  manifestly  be  unjust  to  fail  not 
only  to  lay  upon  them  an  equal  burden,  but  to  charge  them 
even  a  smaller  amount  than  the  average.  The  cost  of  appur- 
tenances, like  manholes,  lamp-holes,  catch-basins,  and  flush- 
ing-tanks, is  sometimes  met  by  the  city  and  sometimes 
included  in  the  cost  of  the  sewer  and  so  distributed.  The 
disposition  of  these  expenses  depends  upon  the  provisions  of 
law.  House-connections  with  the  sewer  are  made  at  the 
expense  of  the  property.  In  addition  a  few  cities  impose  a 
special  charge  for  the  privilege  of  connection  for  the  purpose 
of  increasing  the  sewerage  fund  of  the  city,  but  this  is  to  be 
deprecated  as  tending  to  discourage  the  general  use  of  the 
sewers,  which  has  become  a  sanitary  necessity  in  cities. 

"  The  question  of  the  distribution  of  the  cost  of  a  sewer 
system  is  also  a  complicated  one,  whether  considered  in  the 
light  of  practice  or  principle.  All  the  city  has  an  interest, 
both  general  and  sanitary,  in  its  sewers,  and  the  property- 
owners  have  a  direct  interest  as  abutters  as  well  as  a  particu- 
lar, but  more  general,  one  in  the  larger  mains  of  their  district 
sewers.  As  far  as  the  trunk  sewers  are  concerned,  their  con- 
struction is  of  more  general  import  to  the  city  as  a  whole  than 
to  any  individual  users,  and  their  cost  might  well  be  paid  by 


SPECIFICATIONS,  CONTRACT,  ESTIMATE  OF   COST.       229 

general  taxation.  Whether  or  not  the  city's  share  in  building 
sewers  should  always  be  devoted  to  these  mains,  because  they 
have  the  least  direct  connection  with  property,  may  be 
uncertain,  as  custom  or  local  usage  may  dictate  the  assump- 
tion of  the  cost  of  work  on  street  intersections  or  in  front  of 
city  lots,  parks,  and  other  property,  or  other  expenses, 
besides  the  occasional  defaults  that  come  upon  the  city,  all  of 
which  would  probably  equal  the  proportion  suggested.  All 
the  reasons  given  for  considering  it  equitable  for  the  city 
to  share  in  the  expense  of  its  water-works  system  apply 
equally  to  its  sewer  system;  where  there  are  no  storm-water 
sewers  (a  separate  system)  for  which  the  city  usually  pays,  it 
is  but  just  that  the  city  should  aid  in  the  construction  of  the 
more  usual  combined  system,  which  has  to  receive  the  storm- 
water  from  the  streets.  It  would  be  unfair  to  expect  lots  or 
lands  so  distant  that  they  may  not  be  able  for  years  to  secure 
connection  with  the  system  as  it  develops  to  contribute  much 
toward  paying  for  trunk  sewers  which  will  at  best  be  of  only 
indirect  special  advantage  to  them ;  and  it  is  believed  that  the 
city  assuming  a  share,  to  the  extent  of  20  or  30  per  cent  of 
the  cost  of  its  sewer  system,  would  furnish  but  a  fair  equiva- 
lent for  its  benefit,  and  make  less  burdensome  the  individual 
assessments  which  so  frequently  cause  objection  and  retard 
the  construction  of  these  necessary  improvements. 

"  Of  the  methods  followed  perhaps  the  most  adequate 
plan  of  dealing  with  the  portion  of  the  expense  of  sewers  that 
is  to  be  assessed  is  that  common  one  of  considering  together 
all  the  sewers  of  each  sewer  district  and  distributing  the  cost 
over  the  district  in  proportion  to  the  advantage  received.  In 
many  cities  this  allotment  is  attempted  by  the  frontage  rule, 
but  deep  lots  generally  have  a  larger  share  in  the  use  of 
sewers  than  have  shallow  ones  of  the  same  frontage.  The 
amount  of  storm-water  to  be  removed  from  lots  is  far  from 
having  a  definite  relation  to  frontage,  and  other  irregularities 


230  SEWERAGE. 

result.  Other  cities  apportion  this  assessment  by  the  area 
rule,  but  of  equal  areas  that  which  has  the  greater  frontage 
enjoys  conditions  favoring  a  larger  number  of  buildings  or 
other  improvements  which  imply  a  greater  interest  in  the 
sewer  system,  and  therefore  should  furnish  a  correspondingly 
larger  contribution;  and  as  systems  are  often  built  a  portion 
at  a  time,  lands  remote  from  the  constructed  portions  should 
not  be  required  to  pay  equally  with  lots  that  are  enabled  to 
make  use  of  them  at  once. 

"  In  consequence  of  the  inequitable  features  inhering  in 
both  systems,  in  numerous  instances  it  has  become  an  im- 
proved method  to  combine  the  two  processes  and  assess  40  per 
cent,  more  or  less,  by  frontage  and  the  balance  by  the  area 
rule,  or  to  apply  some  equivalent  procedure  that  will  effect  a 
similar  combination  of  methods.  This  system  of  apportion- 
ment is  growing  in  favor.  It  corrects  the  more  serious  errors 
of  either  method  used  alone.  It  is  not  complex  in  applica- 
tion, and  in  principle  it  is  as  definite  and  as  easily  understood 
by  the  people  affected  as  either  single  process.  Probably  no 
more  adequate  plan  for  sewer  assessments  has  been  exten- 
sively used  than,  after  the  city  has  contributed  its  due  por- 
tion, assessing  by  frontage  an  amount  equal  to  the  cost  of  a 
smaller  size  of  pipe  upon  abutting  property,  as  previously 
mentioned,  or  an  equivalent  amount,  and  distributing  the 
remainder  in  proportion  to  area. 

"  In  some  Massachusetts  cities  the  plan  has  been  ap- 
plied of  partly  paying  the  cost  of  the  sewer  system  and  its 
maintenance  by  a  sewer  rental  corresponding  in  its  principle 
to  the  water  rates  of  water-works  systems.  The  private  con- 
tribution to  sewerage  construction  should  correspond  very 
closely  to  the  use  made  of  them;  and  to  effect  this  Brockton 
and  other  Massachusetts  towns  have  adopted  the  plan  of  such 
an  annual  charge  depending  upon  the  amount  of  water  used, 
claiming  that  the  quantity  of  sewage  to  be  disposed  of  can  be 


SPECIFICATIONS, .CONTRACT,  ESTIMATE  OF  COST.       231 

approximately  estimated  by  reference  to  the  water  rate.  If 
this  plan  does  not  tend  to  discourage  the  use  of  sewers,  if  it 
does  not  too  much  complicate  the  system  of  assessment  and 
proves  otherwise  practicable,  it  may  furnish  a  valuable  addi- 
tion to  the  methods  of  apportionment."  J.  L.  Van  Ormun, 
Transactions  Am.  Soc.  C.E.,  Vol.  XXXVIII. 

Since  the  assessment  is  strictly  a  legal  function  the  State 
laws  and  city  charter  will  to  some  extent  control  the  methods 
in  each  particular  case.  For  instance,  in  New  Jersey  assess- 
ment by  the  front  foot  has  been  decided  illegal.  It  is  prob- 
able that  in  all  States  it  is  legal  to  assess  in  proportion  to 
benefits  received,  and  this  too  would  seem  to  be  demanded 
by  fairness.  (But  in  some  cases  the  courts  have  held  sewerage  to 
be  an  exercise  of  police  power,  and  assessments  legal  where  no  direct 
benefits  accrued.)  These  benefits  consist  of :  (i)  removal  of  house- 
sewage  from  the  buildings;  (2)  removal  of  rain-water  from 
premises  and  streets  (where  combined  or  storm  sewers  are 
built);  (3)  draining  the  land  when  wet;  (4)  increasing  the 
value  of  property;  (5)  a  general  public  benefit  to  the  entire 
city,  whether  it  is  all  sewered  or  not,  consequent  on  the  im- 
proved healthfulness  of  certain  sections,  on  increased  valua- 
tion and  therefore  reduced  tax  rates,  and  on  the  recommen- 
dation to  prospective  residents  that  it  '*  has  sewers."  The 
1st,  3d,  and  4th  are  individual  benefits,  the  2d  a  combination 
of  individual  and  general,  the  5th  a  general  one.  It  would 
appear,  therefore,  that  a  perfectly  just  apportionment  of  the 
cost  would  assess  part,  but  only  a  part,  of  this  upon  property 
directly  benefited,  and  this  at  fixed  rates  in  proportion  to 
front  foot  and  area  combined,  with  an  additional  charge  for 
each  connection  made  or  an  annual  rental  in  lieu  thereof. 
This  charge  may  be  collected  either  as  an  assessment,  to  be 
paid  at  once  or  to  bear  interest  and  be  apportioned  into  sev- 
eral annual  payments;  or  in  the  form  of  rentals,  at  fixed  rates 
for  the  different  classes  of  sewage-contributors  or  else  propor- 


232  SEWERAGE. 

tioned  to  some  function  of  the  water-consumption.  The 
method  employed  at  Maiden,  Mass.,  of  giving  each  property- 
holder  the  option  of  either  of  these  methods  has  some  advan- 
tages. It  is  in  most  cases  desirable  to  make  each  assessment 
or  rental  operative  as  soon  as  it  becomes  possible  to  connect 
the  property  with  the  sewer  and  make  use  thereof,  as  tend- 
ing to  hasten  the  general  use  of  the  system.  Whatever  the 
method  it  should  be  simple  of  application  and  readily  under- 
stood, should  not  be  burdensome  to  the  poorer  property- 
holders,  and  should  encourage  early  and  general  use  of  the 
sewers. 

For  descriptions  of  various  methods  employed  see  the 
paper  quoted  from  above,  Report  of  the  Engineer  to  the 
Brockton  Sewerage  Commission,  and  Journal  of  the  Associa- 
tion of  Engineering  Societies  for  January  and  March,  1897. 


PART  II. 

CONSTRUCTION. 


CHAPTER  IX. 
PREPARING   FOR  CONSTRUCTION. 

ART.  54.     CONTRACT  WORK  OR  DAY  LABOR. 

THERE  are  two  general  plans  by  which  a  city  or  town  may 
construct  a  sewerage  system,  viz.,  by  contract  or  by  day 
labor.  In  a  majority  of  instances,  probably  a  very  large  one, 
the  contract  method  is  adopted,  but  in  quite  a  number  the 
work  is  done  under  the  general  charge  of  the  city  engineer  or 
a  special  agent  or  committee  who  purchases  material,  employs 
labor,  and  looks  after  the  work  generally.  If  the  work  can  be 
kept  entirely  free  from  politics  and  conducted  without  "  fear 
or  favor  "  by  a  good  manager  experienced  in  this  line  of  work 
the  latter  method  will  probably  be  the  more  economical  for 
the  city  and  give  the  more  satisfactory  results.  Unfortu- 
nately these  conditions  exist  in  few  cities  or  towns,  and  the 
contract  method  is  usually  the  cheaper  one,  and  frequently 
gives  better  results  than  construction  by  home  labor  under 
foremen  too  often  unskilled  in  sewerage-work.  There  may 
be  cases  where,  even  with  and  in  spite  of  the  existence  of  the 
above  objections,  construction  directly  by  the  city  is  prefer- 
able. For  instance,  the  work  may  be  of  an  uncertain  nature, 

233 


234  SEWERAGE. 

its  details  difficult  to  foresee  and  set  forth  in  a  contract;  or  it 
may  be  unusually  hazardous,  causing  contractors  to  add  100 
or  even  200  per  cent  to  the  estimated  cost  to  balance  the  risk, 
which  risk  the  city  might  think  it  better  to  assume  itself.  In 
some  instances  villages  have  undertaken  sewerage-work  as  a 
means  of  giving  employment  in  unusually  hard  times  to 
citizens,  who  would  thus  be  enabled  to  pay  part  of  their  wages 
back  to  the  treasury  in  taxes,  and  also  relieve  the  poorhouse 
of  a  large  number  of  possible  inmates. 

Since,  however,  sewerage-work  is  generally  done  by  con- 
tract, the  succeeding  chapters  will  be  made  applicable  particu- 
larly to  construction  by  this  method.  But  the  matter  is 
equally  applicable  to  work  done  by  the  city  or  its  immediate 
agent,  which  agent  should  conduct  the  work  as  the  contractor 
would  have  been  compelled  to  conduct  it. 

It  may  be  sometimes  advisable  for  the  city  to  purchase 
the  materials  and  contract  for  the  labor  of  construction.  In 
this  way  the  quality  of  the  materials  is  under  the  immediate 
control  of  the  city.  In  the  matter  of  cost  there  is  usually 
very  little  difference  one  way  or  the  other,  unless  it  be  that 
the  city  is  charged  a  little  more,  owing  to  a  "  commission  " 
which  must  be  paid  to  certain  officials  who  control  the  award- 
ing of  the  contracts  for  material.  It  is  an  excellent  plan  for 
the  city  to  furnish  cement,  sand,  and  pipe,  and  see  that  there 
is  no  unnecessary  waste  of  these.  There  is  then  no  tempta- 
tion for  the  contractor  to  use  defective  material  or  too  little 
cement. 

Systems  have  been  built  by  letting  the  contract  for  exca- 
vation to  one  party,  and  that  for  pipe-laying  and  brick-work 
to  others,  the  material  being  purchased  by  the  city.  This  is 
almost  sure  to  work  unfavorably  to  the  city  and  give  rise  to 
the  greatest  confusion,  of  responsibilities  if  not  of  work. 


PREPARING   FOR    CONSTRUCTION.  235 


ART.  55.     OBTAINING  BIDS. 

If  work  is  to  be  let  by  contract  the  probabilities  are  that' 
the  greater  the  number  of  bidders  the  lower  will  be  the  sum 
for  which  the  work  can  be  constructed,  a  partial  cause  of  this 
being  the  lessened  liability  of  collusion  between  the  bidders. 
To  reach  contractors  two  methods  are  open:  to  send  notice  to 
individual  contractors,  or  to  advertise  in  such  a  way  and  place 
as  will  attract  the  attention  of  a  large  number.  Each  method 
has  its  advantages,  and  perhaps  a  combination  of  the  two 
might  give  the  best  results.  But  it  is  probable  that  one  or 
two  advertisements  judiciously  placed  will  reach  all  who  would 
be  reached  by  the  first  method,  and  many  others  besides. 
For  a  small  village  the  best  advertising  medium  is  the  con- 
tractors' journal  having  the  widest  circulation  in  that  part  of 
the  country,  which  is  also  true  for  a  city  if  the  work  amounts 
to  more  than  a  very  few  thousand  dollars.  For  small  con- 
tracts in  cities  having  several  capable  contractors  among  its 
citizens  the  local  paper  will  perhaps  give  sufficient  publicity 
to  the  desire  for  bids,  but  village  papers  are  generally  useless 
for  this  purpose.  For  contracts  of  $5000  or  more  an  adver- 
tisement in  one  or  two  prominent  engineering  and  contracting 
papers  will  usually  pay  for  itself  many  times  over. 

The  customary  method  of  bidding  is  to  have  each  con- 
tractor submit  a  sealed  proposition,  all  of  these  being  opened 
at  a  time  fixed  beforehand.  It  would  be  unfair,  if  not  illegal, 
to  open  any  sealed  bid  before  this  time  or  to  receive  another 
bid  after  any  had  been  opened.  To  satisfy  both  the  public 
and  the  contractors  of  the  honesty  and  fairness  of  the  award- 
ing of  the  contract  it  is  customary  to  open  the  bids  and  read 
them  aloud  at  a  meeting  open  to  the  public,  or  at  least  to  all 
bidders  and  to  newspaper  representatives.  The  opportunities 
for  dishonesty  are  so  great  if  the  bids  are  opened  in  secret  or 


236  SEWERAGE. 

one  received  after  others  have  been  read  that  regard  for  their 
own  reputations  usually  influences  the  officials  making  the 
award  to  adopt  the  above  methods. 

That  there  may  be  no  informal  or  incomplete  bids  it  is 
desirable  that  all  bids  be  made  on  forms  furnished  by  the  city 
and  accompanied  by  copies  of  the  specifications  and  contract 
similarly  furnished.  It  would  be  possible  for  a  bidder  whose 
bid  had  been  accepted  to  refuse  to  contract  for  the  work 
unless  he  were  bound  in  some  way.  For  this  reason  it  is  well 
to  require  that  each  bid  be  accompanied  by  a  certified  check, 
to  be  returned  to  the  bidder  unless  he  refuse  to  sign  the  con- 
tract based  upon  his  bid,  if  so  requested. 

The  laws  of  different  States  and  cities  differ  as  to  the  lati- 
tude given  in  awarding  contracts.  In  some  the  contract  must 
be  awarded  to  the  "  lowest  bidder,"  in  others  to  the  "  lowest 
responsible  bidder,"  while  in  still  others  there  is  no  restric- 
tion. Justice  to  the  taxpayers  and  fairness  to  the  bidders 
will  usually  dictate  awarding  to  the  lowest  bidder,  unless 
there  be  reason  to  think  that  he  will  be  unable,  through 
inexperience,  to  do  creditable  work,  or  that,  his  bid  being 
lower  than  the  work  can  probably  be  done  for,  he  will  later 
abandon  the  work,  and  the  consequent  delay  and  legal  com- 
plications, even  though  his  bond  insure  the  ultimate  comple- 
tion of  the  contract,  will  be  detrimental  to  the  city's  interests. 
If  it  becomes  evident  during  construction  that  the  contractor 
cannot  but  lose  money  there  is  usually  a  tendency  to  favor 
him  in  minor  matters,  to  grant  him  extensions  of  time  and 
aid  him  in  other  ways  which  detract  more  or  less  from  the 
excellence  of  the  work.  In  order  to  avoid,  on  the  other  hand, 
the  necessity  of  awarding  the  contract  to  a  too  high  bidder 
when  there  are  no  reasonably  low  ones  the  city  should 
"  reserve  the  right  to  reject  any  or  all  bids." 


PREPARING   FOR    CONSTRUCTION.  237 


ART.  56.     ENGINEERING  WORK  PRELIMINARY  TO 
CONSTRUCTION. 

As  soon  as  possible  after  the  signing  of  the  contract  the 
contractor  should  submit  samples  of  the  material  he  wishes 
to  use,  and  these  should  be  carefully  examined  by  the 
engineer,  and  if  accepted  should  be  retained  and  marked  for 
future  identification  and  compared  from  time  to  time  with 
the  material  actually  furnished. 

The  contractor  should  be  notified  some  days  in  advance 
of  the  point  or  points  at  which  he  is  to  begin  work.  Reason- 
able deference  should  be  made  to  his  wishes  in  this  matter, 
since  it  is  his  privilege  and  duty  to  so  organize  the  work  as  to 
secure  the  greatest  efficiency  at  the  least  cost  to  himself.  If, 
for  instance,  part  of  the  work  lies  through  wet  ground  and 
sub-drains  are  to  be  used  it  is  ordinarily  to  his  interest,  and 
indirectly  to  the  city's  also,  that  the  work  begin  at  an  outlet 
to  which  all  ground-water  will  drain,  or  at  a  point  at  which  a 
pump,  once  set  up,  can  drain  the  work  for  long  distances 
without  moving  its  location,  as  at  the  junction  of  two  mains. 
It  is  also  usually  desired  by  the  contractor  that,  if  two  or 
three  small  gangs  are  to  work  at  as  many  places,  they  may  be 
within  a  few  blocks  of  each  other  for  convenience  of  oversight. 
It  will  ordinarily  be  to  the  interests  of  both  contractor  and 
city  to  work  in  as  dry  ground  as  possible,  and  hence  to  leave 
until  summer  droughts  construction  through  low,  soggy  land. 
Construction  across  or  near  streams  should  not  be  carried  on 
when  there  is  a  possibility  of  floods  or  freshets,  if  it  can  be 
avoided.  Both  trench-  and  masonry-work  should  be  avoided 
in  winter  weather  if  possible,  for  it  is  then  costly  to  the  con- 
tractor, and  it  is  impossible  to  be  sure  that  the  mortar  is 
uninjured,  or  to  restore  the  streets  to  good  condition  with 
frozen  earth. 


233  SEWERAGE. 

Ordinarily  the  contractor  will  desire  to  place  upon  the 
street,  along  the  line  of  the  work,  pipe,  brick,  sand,  lumber, 
etCo  This  cannot  be  denied  him,  but  he  should  be  compelled 
to  place  and  pile  this  material  so  as  to  interfere  with  travel  as 
little  as  possible,  and  along  only  those  stretches  of  street  in 
which  construction  is  to  be  begun  within  a  week,  or  ten  days 
at  the  outside.  This  material  should  be  inspected  as  it  is 
delivered,  and  that  condemned  removed  at  once. 

Just  before  the  work  begins  it  is  well  to  run  levels  care- 
fully over  all  bench-marks  to  see  that  they  have  not  been 
disturbed  and  to  check  previous  levelling;  also  to  establish 
new  ones  if  necessary.  It  is  desirable  to  so  place  these  that 
one  of  them  can  be  seen  from  the  instrument  when  set  up  for 
giving  grades  to  any  part  of  the  work.  They  should  be 
accurate  within  at  least  .003  of  a  foot. 

ART.  57.     OTHER  PRELIMINARIES. 

Final  arrangements  should  now  be  made  for  the  oversight 
of  the  work,  the  proper  instruments  obtained,  engineering  and 
inspecting  assistants  engaged,  an  office  or  other  headquarters 
arranged  for,  notebooks  and  blanks  obtained  for  making  and 
preserving  records,  final  arrangements  made  as  to  right  of  way 
across  private  property  and  along  county  roads  or  others  not 
controlled  by  the-  city  or  village.  Arrangements  should  be 
made  also  for  locating  the  branches  for  house-connections  at 
the  points  desired  by  the  property-owners.  For  this  purpose 
it  is  well  to  publish  in  the  paper  or  otherwise  make  known  to 
the  citizens  that  each  is  desired  to  drive,  at  his  fence-line  or 
curb,  a  stake  indicating  the  point  at  which  he  wishes  his 
house-connection  to  enter  his  property,  and  that  in  case  no 
such  stake  is  driven  the  engineer  or  inspector  will  use  his 
judgment  in  locating  such  branches.  Another  method  is  that 
af  requesting  that  sketches  of  the  property  showing  such 


PREPARING   FOR    CONSTRUCTION,  239 

point  be  handed  in  on  blanks  to  be  furnished  by  the  engineer; 
but  the  inability  or  hesitancy  of  many  citizens  to  make  the 
simplest  drawing  is  an  objection  to  this  plan. 

Counsel  for  the  city  should  pass  upon  the  sufficiency  and 
correctness  of  the  contracts  signed,  of  the  bonds  given  and  of 
their  signers,  and  all  other  legal  matters  in  connection  there- 
with, before  the  contractor  is  permitted  to  begin  work. 


CHAPTER   X. 
LAYING  OUT   THE   WORK. 

ART.  58.     LINING  OUT  TRENCHES. 

SINCE  the  trench  is  seldom  more  than  6  inches  wider  on 
each  side  at  the  bottom  than  the  sewer  to  be  placed  in  it,  it 
is  necessary  that  the  trench  itself  be  carefully  aligned,  and 
this  cannot  be  entrusted  to  the  contractor  except  for  short 
distances.  For  giving  him  the  line  the  safest  plan  is  to  drive 
stakes  or  spikes  along  the  centre  of  the  proposed  trench  at 
intervals  of  about  50  feet.  To  assist  in  finding  these,  for 
checking,  and  to  locate  the  centre  of  the  sewer  during  con- 
struction, the  distance  should  be  taken  from  each  of  these  to 
the  curbing  opposite,  if  there  is  any,  or  to  a  reference-stake, 
and  a  note  made  of  this.  The  centre  spikes  or  stakes  should 
be  some  uniform  distance  apart  to  facilitate  rinding  them. 
They  should  be  set  by  a  transit  placed  over  the  centre  of  a 
manhole  on  the  line.  The  line  should  of  course  be  straight 
between  manholes,  except  in  the  case  of  large  sewers,  which 
may  be  curved,  in  which  case  the  centre  stakes  should  be  set 
not  more  than  25  feet  apart.  The  location  of  manholes,  flush- 
tanks,  etc.,  should  be  fixed  by  two  or  more  reference-stakes  and 
pointed  out  to  the  contractor  before  he  begins  excavating,  that 
he  may  make  allowance  for  them  in  sheathing. 

Some  engineers  in  giving  line  rely  entirely  upon  reference - 

stakes  placed  a  uniform  distance  from  the  center  of  the  trench, 

240 


LAYING    OUT    THE    WORK.  241 

because  the  centre  stakes  will  be  removed  in  excavating.  An 
experience  with  the  unreliability  of  contractors'  tapes  and 
foremen's  intelligence  seems  to  argue  in  favor  of  the  centre 
stakes,  however. 

It  is  well  to  do  a  large  part  of  this  lining  out  before  con- 
struction gets  well  under  way,  since  it  is  probable  that  the 
engineer  corps  will  be  kept  busy  with  other  work  later.  Each 
line  should  be  located  only  after  due  consideration  of  the 
points  referred  to  in  Art.  29. 


ART.  59.     GIVING  GRADE. 

Several  methods  of  giving  grade  are  employed  by  different 
engineers,  the  principal  being:  By  means  of  a  cord  stretched 
over  the  centre  of  the  trench  and  parallel  to  the  sewer  grade; 
by  stakes  driven  to  grade  along  the  centre  line  in  the  bottom 
of  the  trench;  and  by  stakes  driven  at  the  ground-surface  near 
the  edge  of  the  trench,  their  tops  a  uniform  or  stated  distance 
above  the  sewer  grade.  (The  grade  used  in  both  designing 
and  construction  is  that  of  the  inside  bottom  of  the  invert, 
which  for  convenience  will  be  called  the  invert.)  Each  of 
these  is  used  for  both  pipe  and  brick  sewers,  but  only  the  first 
method  is  at  all  adapted  to  accurate  laying  of  pipe  sewers. 
For  brick  sewers  either  method  may  be  used,  but  the  first  is 
most  convenient  in  that  the  invert-templet  can  be  set  at  any 
point  along  the  trench,  and  that  the  bottom  of  the  trench  can 
be  carried  to  the  exact  grade  at  every  point,  in  advance  of 
setting  the  templet,  by  measuring  down  from  the  cord.  If 
stakes  are  driven  in  the  bottom  the  templets  can  be  accurately 
set  only  at  points  close  to  these,  and  the  stakes  can  be  driven 
only  when  the  bottom  is  within  a  foot  or  less  of  grade,  which 
necessitates  the  presence  of  the  engineer  upon  the  work 
almost  constantly.  If  the  stakes  are  driven  along  the  edge  of 


242 


SEWERAGE. 


the  trench  they  can  be  set  even  before  the  excavation  has 
been  begun,  enough  for  several  days  in  advance  being  set  at 
one  time;  but  it  is  almost  impossible  to  avoid  errors  in 
measuring  down  from  these,  since  they  are  not  directly  above 
the  sewer,  and  the  stakes  are  apt  to  become  loose  or  fall  out 
with  the  cracking  and  caving  of  the  edge  of  the  trench. 

The  cord  used  in  the  first  method  may  be  fastened  to  a 
strip  of  wood  nailed  in  a  vertical  position  to  a  plank  which 
stands  upon  edge  with  one  end  resting  upon  the  ground  on 
each  side  of  the  trench.  This  plank  should  extend  at  least  18 
inches  or  2  feet  beyond  the  trench  on  each  side  and  be  firmly 
bedded  into  solid  ground  so  that  it  cannot  possibly  settle,  and 
should  be  held  upright  on  edge  by  a  stake  driven  on  each  side 
at  each  end,  or  by  stones  and  earth  solidly  banked  around  the 
ends.  These  grade-planks  should  be  not  more  than  33^-  feet 


FIG.  6. — METHOD  OF  SETTING  GRADE-PLANK. 

apart — 25  feet  would  perhaps  be  better,  since  the  cord  will  sag 
too  much  if  the  distance  between  supports  be  greater.  On 
the  top  edge  of  these  planks  the  centre  of  the  trench  is 
marked,  and  strips  of  wood  about  I  inch  X  2  inches  X  24 
inches  are  nailed  so  that  one  edge  of  each  is  in  this  centre  line 
and  truly  vertical,  as  determined  by  a  plumb-bob.  On  this 
edge  is  placed  a  mark  exactly  a  whole  number  of  feet  above 
the  sewer-invert  immediately  beneath,  and  a  slight  notch  is 
cut  to  receive  the  cord.  All  notches  in  a  given  length  of 


LAYING    OUT    THE    WORK. 


243 


sewer  are  placed  the  same  distance  above  the  sewer-invert, 
and  the  cord  stretched  from  one  to  the  other  is  therefore 
parallel  to  the  grade,  which  can  be  found  at  any  point  by 
measuring  the  given  fixed  distance  down  from  the  cord.  The 
cord  is  also  vertically  above  the  centre  line  of  the  sewer.  If 
the  trench  changes  in  depth  or  for  some  reason  it  is  desirable 
to  change  the  distance  from  the  cord  to  the  sewer-invert,  a 
step  up  or  down  must  be  made  at  some  grade-plank  by  cutting 
two  notches  one  or  two  feet  apart  in  elevation.  The  cord 
should  be  strong  linen  fish-line  or  similar  material  whose  light 
weight  will  prevent  unnecessary  sagging,  and  should  be 
stretched  tightly  between  the  grade-planks. 

Another  method  of  supporting  the  string  is  to  drive  at 
equal  intervals  stout  stakes,  at  least  2  inches  X  4  inches  X  5 


FIG.  7. — METHOD  OF  SETTING  GRADE-PLANK. 

feet  in  dimension,  on  each  side  of  and  about  3  feet  back  from 
the  trench,  and  in  pairs  directly  opposite  each  other.  On  each 
of  these  is  found  a  point  a  certain  whole  number  of  feet  above 
the  sewer-invert  and  usually  2  or  3  feet  above  the  ground, 
and  a  straight-edged  board  or  plank  is  nailed,  one  end  to  each 
stake,  with  its  upper  edge  exactly  at  these  points.  On  this 
edge  is  marked  the  centre  of  the  trench  and  a  slight  notch 
cut  there  to  receive  the  cord.  One  end  of  the  cord  is  fastened 
to  a  nail  driven  into  the  first  board  below  the  notch,  and  rests 


244 


SE  WERA  GE. 


in  this  notch  and  those  of  succeeding  boards,  and  is  fastened 
at  its  other  end  to  another  nail  placed  as 
is  the  first.  Or  a  large  spool  is  cut  as 
shown  in  Fig.  8  and  caught  behind  the 
board,  the  cord  being  fastened  in  it  and 
being  readily  tightened  whenever  it  be- 
comes loose.  This  method  of  elevated 

FIG.    8. — METHOD    OF 

HOLDING     GRADE-  grade-boards    is  particularly  applicable  to 

large  pipe  sewers  or  small  brick  ones,  since, 
the  cord  being  higher  above  the  ground,  it  interferes  less  with 
the  lowering  of  materials  into  the  trench.  In  some  cases  it  is 
not  wise  to  adopt  it  on  account  of  the  liability  of  the  banks  to 
be  caved  in  by  the  driving  of  the  posts. 

In  laying  pipe  sewers  from  the  cord  a  grade-rod  is  used 
with  a  mark  or  notch  on  its  edge  so  placed  that  when  it  is 
level  with  the  string  the  foot  of  the  rod  is  level  with  the  sewer- 
invert  or  with  the  outside  top  of  the  pipe.  The  former  is  prefer- 
able, since  the  invert  is  the  part  of  the  pipe  which  it  is  most 
important  to  have  at  correct  grade,  and,  as  the  pipes  often 
vary  slightly  in  diameter,  this  result  may  not  be  obtained  if 
they  are  graded  by  their  tops.  If  the  inverts  are  to  be  set 
it  will  be  necessary  to  have  an  offset-piece 
at  the  foot  of  the  grade-rod  which  can 
rest  inside  the  pipe  upon  the  invert.  For 
this  purpose  an  ordinary  cast-iron  6-  or 
8-inch  bracket,  obtainable  at  any  hard- 
ware-store, will  answer;  or  wrought  iron 
may  be  used  if  about  J  inch  thick  and 
stiffened  by  being  bent  back  upon  the 
rod.  The  latter  is  probably  the  more  dur- 
able. The  mark  on  the  grade-rod  should  be 
checked  each  day. 

For  brick  sewers  each  templet  is  set  by  a  rod,  and  for  both 
these  and  pipe  sewers  another  rod  is  used  by  the  foreman  for 
getting  the  excavation  to  the  proper  depth. 


FIG.  9. — GRADE-ROD. 


LAYING    OUT    THE    WORK.  545 

The  grade-plank  or  stakes  above  described  can  be  set  out 
even  before  excavation  is  begun,  but  except  in  shallow 
trenches  it  is  better  to  wait  until  the  trench  is  at  least  6  feet 
deep,  that  they  may  interfere  with  the  excavating  as  little  as 
possible.  It  is  often  well,  however,  to  drive  the  stakes,  where 
these  are  used,  before  excavating  to  prevent  cracking  the 
bank,  the  board  not  being  nailed  to  them  until  afterward. 
The  grade-plank  and  stakes  should  be  tested  for  grade  and 
line  at  least  once  a  day,  and  the  inspector  should  keep  close 
watch  of  them  to  see  that  they  are  not  disturbed  and  also 
that  the  cord  is  kept  taut. 

When  excavating-machinery  is  used  the  grade-planks 
cannot  ordinarily  be  placed  above  the  surface,  but  they  can 
be  sunk  into  the  ground  entirely  below  the  surface,  or  the 
bracing  of  the  trench  can  be  utilized  by  nailing  the  vertical 
strips  to  it.  This  latter  method  is  also  preferable  for  pipe 
sewers  when  the  trench  is  very  deep,  since,  if  the  cord  is  at 
the  surface,  the  grade-rod  is  too  long  for  convenience  and 
accuracy,  and  the  inspector  is  too  far  from  the  work  of  sewer 
•construction  to  watch  properly  both  it  and  the  grade-rod. 

In  trenches  through  running-  or  quicksand  unless  the 
utmost  care  is  taken  the  banks  will  settle  several  inches  or 
even  feet,  carrying  the  grade-plank  with  them  of  course. 
Under  such  circumstances  a  level  should  be  kept  constantly 
on  the  ground  and  the  grades  checked  every  few  minutes 
during  pipe-laying  or  at  the  time  of  setting  templets.  More- 
over, the  bench-marks  themselves,  when  on  curbing,  fire- 
hydrants,  or  elsewhere  near  the  roadway,  may  settle  and 
should  be  checked  daily. 

For  properly  fixing  the  grade  of  a  manhole-head  a  stake 
may  be  driven  near  by  indicating  the  street  grade,  and  it 
would  also  be  well  to  test  the  head  by  the  level  as  it  is  being 
set.  Similar  stakes  should  be  set  for  storm-water  inlets. 


246  SEWERAGE. 

Inlet-  and  house-connections  should  be  laid  as  truly  to  line 
and  grade,  and  in  the  same  way,  as  the  sewer  itself. 

Where  grade-stakes  in  the  bottom  are  used  these  are  set 
to  the  exact  grade  of  the  invert  or  one  foot  above  it.  For 
pipe  sewers  the  bottom  of  the  trench  is  then  given  a  uniform 
grade  from  one  stake  to  another  by  using  a  straight-edge, 
stretching  a  cord,  or  too  often  by  eye  only,  and  the  pipe  is 
laid  on  this  bottom  and  lined  in  by  eye.  Great  accuracy  can 
hardly  be  expected  by  this  method.  For  brick  sewers,  how- 
ever, it  compares  favorably  with  the  cord  for  accuracy  (but 
not  for  convenience),  the  stakes  being  driven  in  the  centre 
line  of  the  sewer  and  at  such  distances  apart  that  each  templet 
can  be  set  close  to  a  stake. 

Stakes  driven  upon  the  bank  are  not  recommended  for  any 
purpose,  it  being  almost  impossible  to  obtain  accurate  results 
by  their  use.  Their  only  advantage  is  that  setting  them 
gives  less  trouble  to  the  engineer  than  either  of  the  other 
methods. 

Alleged  sewers  have  been  laid  with  a  carpenter's  level  2  feet 
long,  to  the  under  side  of  one  end  of  which  was  fixed  a  piece 
of  wood  on  iron  or  a  screw  protruding  an  amount  equal  to  the 
desired  rise  in  that  distance.  It  would  be  an  exceptional  case 
in  which  a  line  of  sewer  so  laid  did  not  vary  more  than  one 
inch  in  each  100  feet  from  the  desired  grade. 

While  giving  grades  the  measurement  of  the  sewer-lines 
should  be  carefully  made  and  noted  and  compared  with  the 
original  measurements,  and  if  any  appreciable  difference  is 
found  the  sewer  grades  upon  the  plans  must  be  readjusted  to 
correspond.  Careful  notes  should  be  kept  of  all  instrumental 
'work  connected  with  giving  line  and  grade.  It  will  be  con- 
venient to  have  in  each  level-notebook  a  list  of  all  bench- 
marks in  the  sewer-district  in  which  it  is  to  be  used. 

Both  inspector  and  engineer  should  watch  for  the  first 
indication  of  the  existence  in  the  trench  of  an  obstruction  to 


LAYING    OUT    THE    WORK.  247 

the  sewer,  that  preparation  may  be  made  for  a  change  *n  line 
or  grade  if  necessary  to  pass  the  obstruction.  Such  change, 
if  in  line,  may  necessitate  inserting  one  or  two  additional  man- 
holes or  a  lamphole;  if  in  grade  it  may  sometimes  be  made  by  a 
decrease  in  grade  in  one  stretch  and  an  increase  in  the  next, 
or  by  siphoning  under  or  over  the  obstruction  (see  Art.  44). 
In  some  cases  the  change  can  be  made  in  the  obstruction  and 
not  in  the  sewer. 

It  is  the  inspector's  duty  to  see  that  house-  and  inlet-con- 
nection branches  are  inserted  at  the  proper  points,  and  their 
exact  locations  noted,  which  locations  the  engineer  must  make 
note  of  and  reference  to  some  fixed  point,  usually  the  centre 
of  the  nearest  manhole,  to  make  possible  the  ready  finding  of 
the  branches  in  the  future.  This  is  very  important  and  should 
be  faithfully  attended  to. 

In  addition,  some  engineers  bury  in  the  trench  a  stake  stand- 
ing vertical  above  each  branch  and  rising  to  within  one  or  two 
feet  of  the  surface,  which  can  be  found  by  a  plumber  soon  after 
beginning  to  excavate  for  a  connection. 


CHAPTER    XL 
OVERSIGHT   AND   MEASUREMENT   OF   WORK. 

ART.  60.     INSPECTION  OF  WORK. 

THE  specifications  are  practically  the  instructions  to  the 
contractor  as  to  the  way  in  which  the  sewerage  system  is  to 
be  built,  the  lines,  grades,  and  dimensions  being  given  by  the 
engineer,  chief  or  assistant.  If  the  contractor  were  left 
unwatched  to  carry  out  these  instructions  it  would  be  impossi- 
ble to  know  whether  he  had  done  so  or  not,  since  only  the 
inside  of  the  sewer  can  be  examined,  and  this  only  with  diffi- 
culty. And  if  it  were  found,  after  the  completion  of  the 
work,  that  it  had  been  improperly  built  or  of  poor  material, 
even  though  the  contractor  could  be  compelled  to  replace  it 
with  satisfactory  work,  the  delay  and  inconvenience  of  this 
might  better  be  avoided  by  proper  oversight  during  construc- 
tion. It  is  advisable,  therefore,  that  a  competent  inspector 
be  constantly  on  hand  when  any  construction  is  progressing. 
This  is  not  necessary  during  excavation,  but  even  this  should 
be  looked  after  at  least  once  a  day,  that  any  unforeseen 
underground  condition  which  may  modify  the  plans  may  be 
noted,  and  in  general  to  ascertain  that  the  contractor  is 
obtaining  the  proper  width  of  trench,  is  not  interfering  un- 
necessarily with  private  drains,  water-  or  gas-pipes,  and  is  in 
general  following  the  directions  for  trenching,  blasting,  etc. 

For  this  oversight  it  will  usually  be  necessary  to  have  an 

inspector  for  each  set  of  pipe-layers  and  of  masons.     But  if 

248 


OVERSIGHT  AND    MEASUREMENT   OF   WORK.          249 

only  one  or  two  trenches  are  being  worked  at  a  time  the 
instrument-man  may  also  be  inspector.  The  omissions  and 
poor  work  which  may  be  accepted  from  the  contractor  if  such 
inspection  is  not  constantly  made  may  be  seen  from  a  state- 
ment of  the  inspector's  duty. 

The  inspector  should  be  on  hand  before  work  is  begun  at 
morning  and  noon  to  see  that  no  mortar  left  from  the  previous 
day  is  worked  over,  that  new  mortar  is  properly  proportioned 
and  mixed,  and  to  examine  grade-lines  or  -stakes.  In  the 
case  of  pipe  sewers  he  should  examine  the  inside  of  the  sewer 
near  the  end  and  see  that  any  stones,  dirt,  or  other  matter 
which  may  be  there  be  removed  before  the  laying  begins. 
He  should  also  examine  the  one  or  two  cemented  joints 
nearest  the  end,  and  if  they  are  not  sound  the  pipe  should  be 
removed  and  relayed.  In  the  case  of  brick  sewers  he  should 
examine  the  end  of  the  brick-work  and  have  removed  any  loose 
brick  and  all  mortar  and  dirt  that  may  be  lodged  there. 

He  should  continually  keep  an  eye  upon  material  and 
workmanship,  examining  each  pipe  before  it  is  lowered  into 
the  trench,  each  load  of  brick  and  of  sand  as  they  are  brought 
upon  the  ground,  each  barrel  or  bag  of  cement  to  see  that  it 
bears  the  engineer's  mark  or  is  of  the  required  make  and  that 
it  is  not  caked  by  moisture.  He  should  see  that  the  proper 
proportions  of  cement  and  sand  are  used  for  the  mortar,  and 
that  no  mortar  partially  set  is  retempered  and  used. 

On  brick  sewers  he  should  see  that  each  templet  used  is 
one  approved  by  the  engineer  and  that  it  is  set  to  the  proper 
grade  and  line,  that  the  brick  are  laid  to  line  and  in  accordance 
with  the  specifications,  that  slants  or  other  branches  are  set 
where  needed,  and  he  should  keep  an  accurate  account  of 
these,  their  size  and  length,  and  mark  the  position  of  each  by 
a  stake  driven  in  the  bank  directly  over  it  for  the  information 
of  the  engineer.  He  should  see  that  the  arch-centre  is  solid 
and  does  not  spring  under  the  brick-work,  and  that  it  is  not 
drawn  too  soon. 


250  SEWERAGE. 

In  concrete  sewers  he  should  see  that  the  forms  are  substantial 
and  remain  in  place,  and  do  not  allow  the  escape  of  water  from 
the  concrete;  and  that  all  concrete  is  well  settled  into  place. 
Also  that  set  concrete  and  fresh  are  properly  bonded  together, 
and  that  concrete  is  not  disturbed  in  any  way  until  set. 

On  pipe  sewers  he  should  see  that  each  pipe  is  laid  to 
grade  and  line  by  the  use* of  the  grade-rod  and  a  plumb-bob 
in  connection  with  the  grade-cord,  that  each  pipe  is  pushed 
*'  home,"  each  joint  properly  cemented  and  the  swab  or  piston 
in  the  sewer  pulled  forward,  and  that  the  back-filling  is 
properly  placed  and  tamped  around  the  pipe.  He  should  see 
that  house-branches  are  placed  where  directed,  that  covers 
are  cemented  in  each  one  (about  this  he  is  sometimes  careless, 
to  the  great  detriment  of  the  sewer),  and  should  drive  a  stake 
in  the  bank  directly  over  each. 

He  should  keep  a  record  of  all  extra  work,  or  work,  such 
as  foundations  or  sheathing  left  in  the  trench,  which  cannot 
be  measured  after  the  completion  of  the  sewer. 

If  the  ground  is  wet  he  should  see  that  no  water  flows 
over  the  brick-work  or  through  the  pipe,  except  as  permitted 
by  the  engineer.  In  general  he  should  be  thoroughly  familiar 
with  the  specifications  and  have  a  copy  constantly  on  the 
work,  and  see  to  their  enforcement,  reporting  to  the  engineer 
any  difficulty  in  obtaining  this. 

He  should  not  be  permitted  to  be  in  any  way  indebted  to, 
or  under  the  influence  and  power  of,  the  contractor,  and 
should  receive  orders  from  the  engineer  only. 

He  should  be  a  man  with  some  experience  in  the  character 
of  work  he  is  inspecting,  sober,  and  having  the  respect  of  the 
contractor  and  workmen. 

ART.  61.  DUTIES  OF  THE  ENGINEER. 

The  engineer  or  his  assistant  should  keep  constantly  in  touch 
with  the  work,  visiting  each  point  at  least  once  a  day,  and 


OVERSIGHT   AND   MEASUREMENT    OF    WORK.  251 

giving  necessary  instructions  to  the  contractor  and  inspector 
as  well  as  giving  and  testing  line  and  grade.  If  he  has  many 
inspectors  on  work  under  his  charge  they  should  be  required 
to  report  at  the  engineer's  office  after  each  day's  work  the 
amount  done  and  return  a  detailed  statement  of  any  extra 
work,  asking  instructions  on  any  points  concerning  which  they 
are  in  doubt.  The  daily  reports  may  be  made  in  writing  upon 
blanks  furnished  to  the  inspectors  for  this  purpose. 

The  engineer  must  see  that  each  inspector  is  performing 
his  duty,  and  if  necessary  enforce  instructions  given  by  him 
to  the  contractor.  He  must  inspect  all  material  to  be  used, 
where  this  is  possible,  or  give  the  inspector  full  instructions 
on  this  point  where  it  is  not.  It  is  well  to  mark  each  accepted 
barrel  or  bag  of  cement;  to  inspect  the  pipe  after  it  is  deliv- 
ered upon  the  street,  but  well  in  advance  of  the  laying,  seeing 
that  all  defective  pipe  is  removed ;  also  to  inspect  and  weigh 
all  iron-work  before  it  is  used. 

The  engineer  must  decide  where  and  how  much  sheathing 
shall  be  left  in  the  trench,  making  a  note  at  the  time  of  its 
exact  location  and  amount,  must  decide  as  to  the  classification 
of  the  material  being  excavated,  and  must  measure  promptly 
all  material  classed  as  rock.  He  should  each  day  take  measure- 
ments necessary  to  locate  the  house-branches  as  indicated  by 
the  inspectors'  stakes.  It  is  well  to  measure  each  stretch  of 
sewer,  each  manhole  and  other  appurtenance  as  soon  as  com- 
pleted. 

The  engineer  should  see  that  the  contractor  respects  the 
rights  of  property-owners  and  keeps  the  streets  and  sidewalks 
open  where  possible,  that  the  laborers  are  efficient  and,  where 
necessary,  skilled  in  the  work  to  which  they  are  assigned,  and 
that  they  create  no  disturbance  along  the  streets  in  any  way 
for  which  the  contractor  is  responsible.  He  should  compel 
the  contractor  to  work  with  sufficient  force  and  in  such  a 
manner  as  will  lead  to  the  completion  of  the  work  in  the 
specified  time,  to  place  such  shoring  and  sheathing  as  may  be 


252  SEWERAGE. 

necessary  to  prevent  any  accidents  to  property  or  lives  or  to  t 
the  sewer,  to  provide  pumps  in  sufficient  number  and  of 
ample  size  to  handle  all  ground-water,  and  to  use  excavating- 
machinery  where  necessary.  In  general  he  should  see  that 
the  work  is  carried  on  by  proper  methods,  with  proper 
materials,  with  a  force  and  a  plant  satisfactory  in  both  char- 
acter and  extent,  and  that  the  inspector  enforces  his  directions 
as  to  details. 


ART.  62.     MEASUREMENTS. 

The  specifications  should  state  in  what  way  the  measure- 
ments shall  be  taken  for  each  description  of  work  or  material. 
The  measurements  so  made  for  the  final  estimate  (which  is 
the  name  customarily  given  to  the  measurements  and  calcula- 
tions on  which  is  based  the  final  payment  for  a  piece  of 
work)  should  be  accurately  and  carefully  taken  and  checked 
at  least  once,  as  should  be  the  calculations  based  thereon. 
The  engineer  should  be  able  to  swear  upon  the  witness-stand, 
as  he  may  be  called  upon  to  do,  that  the  final  estimate  is  a 
truthful  and  correct  statement  of  the  work  actually  done. 
Quantities  given  in  this  estimate  should  be  stated  in  the  units 
used  in  bidding  for  the  work. 

Measurement  of  the  sewer  laid  is  usually  made  from  centre 
to  centre  of  manholes,  flush-tanks,  etc.,  not  horizontally,  but 
parallel  to  the  sewer  (the  surface  of  the  street  being  practically 
this  in  most  cases),  no  deduction  being  made  for  branch 
specials  or  the  lengths  of  manholes.  Payment  is  sometimes 
made  uniformly  for  all  depths  of  sewer,  sometimes  varying 
with  varying  depths.  The  latter  seems  the  fairer  way,  par- 
ticularly where  some  lines  contracted  for  may  be  omitted  or 
new  ones  added.  Usually  no  changes  in  price  are  made  for 
less  differences  in  depth  than  two  feet,  the  measurement  being 
made  from  the  surface  to  the  under  side  of  sewer  or  of  foun- 
dation-platform. These  depths  are  ascertained  from  the 


OVERSIGHT  AND    MEASUREMENT   OF   WORK.         253 

profile,  on  which  are  plotted  the  surface  grade  and  the  sewer. 
Since  for  the  original  profile  elevations  were  in  general  taken 
at  loo-foot  intervals  only,  and  as  a  check  on  these,  the  eleva- 
tion of  the  surface  should  be  taken  and  noted  at  each  grade- 
plank  when  grade  is  being  given  for  sewer  construction. 

The  depth  of  each  manhole,  lamp-hole,  and  other  appur- 
tenance should  be  obtainable  from  the  profile,  but  as  a  check 
each  should  be  measured  with  a  levelling-rod  or  tape.  Each 
manhole,  lamp-hole,  flush-tank,  and  inlet  should  be  designated 
by  a  number,  by  which  it  is  referred  to.  It  is  almost  impos- 
sible otherwise  to  correctly  count  and  keep  track  of  these, 
especially  the  manholes,  so  many  of  which  are  each  common 
to  two  lines  of  sewer. 

Inlet-connections  may  be  measured  from  their  upper  end 
to  the  shoulder  of  the  branch  or  slant.  Whatever  the  limits 
to  be  taken  they  should  be  carefully  set  forth  in  the  specifica- 
tions. 

Rock  should  be  measured  before  excavation  in  most 
instances,  although  its  original  surface  can  often  be  judged 
afterward  by  that  showing  along  the  sides  of  the  trench.  If 
the  rock-surface  is  fairly  even  and  uniform  readings  may  be 
taken  at  intervals  of  10  feet;  but  if  it  be  uneven  and  jagged 
these  should  be,  not  at  regular  intervals,  but  wherever  neces- 
sary to  give  accurate  results.  All  measurements,  whether  of 
earth,  rock,  sewer,  or  manhole,  should  be  taken  to  tenths  of 
a  foot.  It  is  customary  to  allow  the  contractor  a  certain 
cross-section  of  trench,  and  pay  him  nothing  for  excess  exca- 
vation nor  deduct  for  a  less  area  of  section.  But  the  trench 
at  the  bottom  should  be  kept  the  full  width  called  for. 

A  final-estimate  book  should  be  kept,  in  which  is  entered 
an  exact  statement  of  each  piece  of  work  as  it  is  completed, 
but  not  before  then.  The  measurements  should  be  classified 
under  the  items  for  which  bids  were  received,  and  the  location 
of  each  given ;  thus : 


254  SEWERAGE. 

8-INCH    SEWER,    8    TO    IO    FEET    DEEP. 

Location.  Length. 

From  manhole  No.  7  to  manhole  No.  8  327.3  ieet 

Between  manhole  No.  8  and  manhole  No.  9         39 -O    " 

8-INCH    X    4-INCH    Y    BRANCHES, 

Location.  Number. 

Between  manhole  No.  7  and  manhole  No.  8  13 

"     8     "         "          "     9  ii 

MANHOLES. 

No.  of  Manhole.  Location.  Depth. 

7  Main  Street,  between  Clinton  and  Madison  9.2 

8  Corner  Clinton  and  Main  streets  9.2 

A  pocket  field-book  should  be  constantly  at  hand,  in  which 
are  entered  all  measurements  taken,  the  points  of  the  begin- 
ning and  ending  of  "  sheathing  left  in  trench,"  of  sub-drains, 
of  foundations,  the  location  of  all  Y's,  the  details  and  quan- 
tities of  "  extras,"  the  location  of  underground  structures  for 
future  reference,  and  the  date  of  beginning  and  ending  of 
construction  on  each  stretch  of  sewer.  These  notes  should 
be  copied  every  evening  into  an  office-book,  since  a  loss  of 
these  data  would  be  serious  and  irreparable.  The  general 
appearance  of  such  notes  is  shown  on  page  259. 

It  is  well  also  to  have  a  pocket  copy  of  the  profile  of  each 
street,  showing  the  sewer  as  designed,  with  size,  grade,  eleva- 
tion, location  of  manholes,  flush-tanks,  and  other  appurte- 
nances. This  method  of  taking  these  data  to  the  field  for  use 
seems  to  be  more  complete  and  convenient  than  copying  them 
down  into  a  notebook. 

According  to  most  contracts  the  contractor  must  be  paid 
monthly,  and  for  this  purpose  monthly  estimates  must  be 
made  by  the  engineer.  He  should  estimate  each  month  the 
total  amount  of  each  item  completed  to  date,  from  which  is 
deducted  the  total  estimated  the  month  previous,  the  differ- 
ence being  the  amount  performed  during  the  month.  This 
method  prevents  the  carrying  ahead  or  accumulation  of  any 
errors  which  may  be  made  in  any  one  monthly  estimate,  which 
errors  are  liable  to  occur  owing  to  the  fact  that  such  estimate 


OVERSIGHT  AND   MEASUREMENT  Of    WORK.         255 


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256  SEWEXAGE. 

must  often  be  made  hastily  and  simultaneously  with  the 
oversight  of  construction-work.  Uncompleted  work  must  be 
estimated  according  to  the  judgment  of  the  engineer  as 
equivalent  to  so  much  completed  work  of  the  same  class. 

For  the  final  estimate  all  measurements  as  given  in  the 
final-estimate  book  should  be  checked  with  the  field-book  and 
in  every  other  way  possible,  and  every  precaution  taken  to 
secure  absolute  absence  of  error  in  measurements  or  calcula- 
tions. As  a  check  upon  the  estimate  it  would  be  well  to 
obtain  from  the  contractor  the  bill  of  pipe,  brick,  and  iron 
used  by  him  upon  the  work,  allowance  of  course  being  made 
for  material  condemned  or  unused. 

ART.  63.     FINAL  INSPECTION. 

The  final  inspection  of  the  work  before  its  acceptance  from 
the  contractor  should  be  thorough,  and  made  by  the  engineer 
in  person  or  by  an  experienced,  trustworthy  assistant.  He 
should  enter  every  flush-tank,  manhole,  inlet,  or  other  appur- 
tenance sufficiently  large  for  this,  taking  its  dimensions,  notic- 
ing whether  the  head  or  grating  is  at  the  proper  level  and 
substantially  set,  the  brick-work  smooth,  the  form  regular, 
the  steps  properly  set  at  the  prescribed  intervals,  that  no 
ground-water  leaks  through  the  brick-work,  that  pipes  passing 
through  the  walls  are  properly  built  in  with  surrounding 
"  bull's-eyes;"  that  the  bottoms  of  manholes  are  formed  ac- 
cording to  instructions,  the  invert-channel  being  straight  or 
with  a  uniform  curve,  of  the  proper  width,  and  its  grade  uni- 
form through  the  manhole  and  of  the  proper  elevation,  and  that 
the  benches  have  the  specified  slope ;  also,  if  there  are  sub- 
drains,  the  hand-holes  should  be  inspected,  and  these  as  well 
as  the  manholes  should  be  free  from  dirt.  Lamp-holes  should 
be  inspected  by  lowering  a  lamp  into  each  and  noting  whether 
it  is  straight  and  vertical,  and  by  seeing  that  the  heads  are 


OVERSIGHT  AND    MEASUREMENT   OF   WORK.          257 

set  according  to  specifications  and  at  the  proper  grade. 
Flush-tanks  should  be  filled  with  water  and  tested  for  tight- 
ness for  at  least  24  hours,  during  which  time  the  water-level 
in  them  should  not  lower  more  than  one  or  two  inches.  If 
automatic  flushing  apparatus  is  set  it  should  be  tested  with  a 
stream  sufficiently  small  to  fill  it  in  not  less  than  24  hours. 
To  expedite  the  test  it  can  be  rapidly  filled  and  discharged 
once  to  test  its  proper  working,  then  rapidly  filled  three 
quarters  way  to  the  discharging-point  and  the  inflowing 
stream  cut  down  to  the  rate  above  mentioned,  to  see  that  the 
siphon  does  not  "  trickle,*'  but  holds  the  water  until  the 
height  is  reached  calculated  to  cause  a  complete  siphoning  of 
the  water  in  the  tank. 

Every  foot  of  sewer  and  inlet-connection  should  be  in- 
spected. Sewers  24  inches  or  over  in  diameter  should  be 
entered  and  each  joint  inspected,  if  they  are  pipe  sewers,  to 
see  that  no  jute  or  cement  protrudes  into  the  sewer  and  that 
there  is  no  leakage.  In  case  of  the  former  the  protruding 
cement  or  jute  should  be  removed;  and  if  there  is  leakage 
this  should  be  stopped,  for  which  purpose  there  may  be  calked 
into  the  joint  from  the  inside  dry  cement  immediately  fol- 
lowed by  jute,  cloth,  or  similar  material  to  hold  it  in  place 
until  set;  or  wooden  wedges,  or  lead  wool  may  be  used.  If 
these  or  similar  methods  fail  it  may  be  necessary  to  uncover 
the  pipe  and  apply  additional  cement  on  the  outside,  backed 
and  supported  by  concrete  if  necessary.  Any  cracked  or 
broken  pipe  should  be  dug  up  and  replaced.  The  branches 
should  be  examined  also  to  see  that  a  water-tight  cover  js  in 
each  one  which  is  not  already  connected  with  a  house-drain. 

If  the  sewer  is  of  brick  the  brick-work  should  be  smooth, 
with  struck  or  pointed  joints  and  without  any  cracks.  To 
determine  whether  the  form  and  dimensions  are  as  specified 
a  skeleton  templet  may  be  used.  If  the  sewer  is  circular  this 
may  consist  of  two  light  rods,  each  of  a  length  equal  to  the 


258  SEWERAGE. 

nominal  interior  diameter,  and  connected  by  a  bolt  passing 
loosely  through  holes  at  the  exact  centre  of  each.  One  of 
these  rods  is  to  be  held  stationary  across  the  sewer  and  the 
other  revolved  upon  the  bolt,  when  each  end  of  the  latter 
should  just  touch  the  sewer  through  the  entire  revolution. 
For  an  egg-shaped  sewer  a  half  templet  may  be  used.  Slants 
or  other  branches  should  be  examined  as  stated  for  pipe 
branches.  Special  attention  should  be  paid 
to  junctions  of  brick  sewers  to  see  that  the 
curves  are  easy  and  uniform  in  plan  and  that 
the  arches  are  strong  and  well  built.  All 
spalls,  bats,  plank,  and  other  refuse  and  dirt 
should  be  removed  from  the  sewers.  If 
brick  sewers  leak  the  joints  may  be  calked, 
as  suggested  for  pipe-sewer  joints.  For 
such  inspections  a  lantern  with  a  reflector  is 
-  desirable,  or  a  large  dry  battery  electric  lamp. 
SHAPED  SEWER.  Inspection  of  small  pipe  sewers  can  be 

made  from  manholes  only.  As  a  test  for  straightness  a  light 
held  at  the  opening  of  the  pipe  in  a  manhole  or  lowered  into 
a  lamp-hole  should  be  distinctly  visible  from  the  next  man- 
hole. Further  inspection  can  be  made  by  the  use  of  mirrors 
from  which  light  is  reflected  into  the  sewer.  The  simplest 
plan  is  to  reflect  the  sunlight  from  a  mirror  held  by  an  assist- 
ant on  the  surface  to  another  mirror  held  by  the  inspector  in 
the  manhole,  who  so  manipulates  his  mirroi  as  to  throw  a 
spot  of  light  onto  each  length  of  the  sewer  in  succession, 
meantime  inspecting  the  same  by  looking  past  the  mirror  into 
the  sewer.  This  generally  requires  that  he  kneel  in  the  man- 
hole upon  the  side  benches,  his  back  to  the  sewer  to  be 
inspected,  his  head  bent  down  until  he  can  see  into  the  sewer, 
and  the  hand  which  holds  the  mirror  thrust  back  between  his 
legs.  It  is  advisable  that  he  have  pads  for  his  knees  if  he 
have  many  sewers  to  inspect  in  this  way.  Apparatus  has 


OVERSIGHT  AND    MEASUREMENT   OF    WORK.          259 

been  devised  for  removing  some  of  the  inconveniences  of  this 
method  by  so  placing  an  additional  mirror  that  the  interior 
of  the  sewer  is  reflected  therein,  and  the  inspector  is  relieved 
of  the  necessity  of  assuming  an  uncomfortable  position.  Such 
an  apparatus  is  described  in  Engineering  News,  vol.  xxxn, 
page  249. 

The  imperfections  most  commonly  found  in  pipe  sewers 
are:  loops  or  ends  of  oakum  or  ridges  of  cement  protruding 
into  the  sewer  at  the  joints;  dirt,  stones,  etc.,  in  the  sewer; 
uneven  grade,  which  can  be  detected  by  allowing  a  small 
amount  of  water  to  flow  through  the  sewer,  which  stream  will 
be  wider  at  the  depressed  and  narrower  at  the  elevated  points; 
ground-water  leaking  in  through  the  joints;  broken  pipe; 
breaks,  at  joints,  in  the  continuity  of  the  invert-surface. 

Broken  pipe  and  leaking  joints  can  only  be  repaired  by  digging 
down  to  the  sewer  (see,  however,  Art.  80).  -Dirt,  stones,  and 
protruding  cement  may  be  removed  by  drawing  a  scraper  through 
the  sewer  by  means  of  a  rope,  or  by  pushing  it  through  by  a  rod 
formed  by  jointing  together  several  shorter  rods  of  a  size  which 
can  be  introduced  through  a  manhole — about  5  feet.  A  stream 
of  water  from  a  fire-hose  nozzle  under  a  good  head  can  be  used  to 
remove  from  a  stretch  of  sewer  not  more  than  300  feet  long  almost 
anything  less  in  size  and  weight  than  a  brick.  The  hose 
while  water  is  passing  through  it  is  so  stiff  that  it  can  be 
pushed  for  a  long  distance  into  the  sewer.  Jute  ends  or 
loops  are  sometimes  difficult  to  remove,  but  can  usually  be 
cut  off  by  a  sharp  knife-blade  fastened  to  a  long  rod,  or 
burned  off  by  putting  under  them  (they  generally  hang  from 
the  top  of  the  sewer)  a  small  lamp  or  candle  similarly  fas- 
tened. Or,  if  there  is  water  flowing  through  the  pipe,  the 
candle  may  be  fastened  to  a  piece  of  wood  or  cork  to  which 
a  string  is  attached  and  floated  down  to  the  desired  point. 
The  exact  distance  from  the  manhole  of  any  defect  can  be 
ascertained  by  counting  the  number  of  pipe  intervening. 


-260  SEWERAGE. 

Sub-drains  should  be  inspected  by  turning  into  each 
stretch  for  a  short  time  all  the  water  it  can  carry  (if  they  are 
not  already  running  full)  and  watching  for  indications  of 
stoppages.  The  apparatus  for  inspecting  sewers  above 
referred  to  may  in  some  instances  be  used  for  sub-drains, 
being  lowered  into  the  sub-drain  hand-hole.  If  any  drain  is 
entirely  stopped  this  may  be  remedied  by  the  use  of  rods, 
fire-hose,  "  pills  "  (see  Art.  85),  etc. ;  or  it  may  be  necessary 
to  locate  the  obstruction  and  dig  down  to  it. 

As  far  as  possible  assurance  should  be  had  by  examination 
that  all  the  conditions  of  the  contract  have  been  carried  out, 
those  having  reference  both  to  the  construction  and  to  the 
more  strictly  business  relations  between  city  and  contractor. 


CHAPTER    XII. 
PRACTICAL   SEWER   CONSTRUCTION. 

SEWER  construction  is  sometimes  undertaken  by  the 
city  under  the  immediate  supervision  of  the  engineer,  who 
should  in  such  a  case  be  well  informed  in  practical  construc- 
tion methods.  He  would  also  be  better  fitted  by  such  infor- 
mation to  design  a  system  and  to  oversee  it  if  constructed  by 
a  contractor.  This  chapter  is  intended  to  give  some  informa- 
tion on  this  subject  based  upon  practical  experience.  It  is 
not  pretended  that  the  entire  field  is  covered,  but  it  is 
thought  that  the  student  and  those  with  little  experience  in 
sewerage-work,  and  perhaps  others,  will  find  the  information 
given  of  considerable  value. 

ART.  64.     ORGANIZING  THE  FORCE. 

The  number  of  men  which  can  be  worked  in  one  gang 
economically  depends  upon  the  character  of  soil,  depth  of 
excavation,  amount  of  ground-water,  manner  of  construction 
of  the  sewer;  also  upon  the  personality  of  the  general  foreman 
and  contractor.  If  the  soil  is  "  rotten,"  with  little  cohesion, 
very  wet,  or  the  trenches  very  shallow,  the  gangs  should  be 
small;  but  if  the  ground  is  dry  and  stands  up  well  or  the 
trenches  are  deep  larger  gangs  can  be  used.  With  the 
increase  in  the  number  of  gangs  comes  increased  difficulty  in 
keeping  them  all  supplied  with  materials  and  tools  and  work- 

261 


262  SEWERAGE. 

ing  to  an  advantage.  Good  foremen  are  a  necessity  if  there 
are  to  be  more  than  two  or  three  gangs,  since  it  may  at  times 
be  necessary  to  leave  them  to  carry  on  their  work  for  days  at 
a  stretch  with  no  more  than  a  hasty  daily  visit  from  the  con- 
tractor or  general  foreman.  A  foreman  who  can  keep  the  men 
faithfully  at  work  without  favoritism  or  making  himself  gen- 
erally hated  by  them,  who  has  sufficient  intelligent  foresight 
to  arrange  their  work  a  day  or  two  ahead,  to  never  be  out  of 
sheathing,  cement,  sand,  brick,  or  other  material,  who  has  a 
practical  knowledge  and  knack  for  overcoming  difficulties,  and 
who  can  be  depended  upon  to  be  sober  from  the  time  the 
work  starts  until  it  ends — such  a  man  is  valuable  upon  sewer- 
age-work. But  if  such  men  cannot  be  had  it  will  be  better 
to  work  only  two  or  three  gangs,  all  of  which  can  be  kept 
under  the  contractor's  or  engineer's  eye. 

The  city  engineer  or  the  contractor,  as  the  case  may  be, 
if  he  does  not  himself  devote  his  entire  time  to  it,  should  have 
a  general  foreman  over  the  entire  work.  There  should  be  a 
foreman  over  each  gang,  and  if  the  number  in  a  gang  exceeds 
30  an  assistant  foreman;  also  in  each  a  water-boy  to  carry 
drinking-water  and  run  errands.  If  the  trenches  need  sheath- 
ing there  should  be  on  each,  under  the  direction  of  the  fore- 
man, from  one  to  three  men  handy  and  experienced  in  such 
work. 

It  will  be  necessary  to  sharpen  the  picks  frequently,  even 
twice  a  day  in  flinty  hard-pan  or  gravel,  and  for  this  purpose, 
as  well  as  to  repair  shovels,  wheelbarrows,  axes,  chains,  etc., 
a  blacksmith  should  be  established  handy  to  the  work.  When 
not  engaged  on  such  repairs  he  can  be  making  manhole-steps, 
calking-irons,  etc. 

There  should  be  a  timekeeper,  if  the  force  is  large,  to 
tak^  the  time  daily  and  make  it  up  for  each  pay-day,  who 
may  also  serve  as  clerk,  keeping  account  of  all  material 
received  and  where  delivered,  ordering  new  when  so  in- 


PRACTICAL   SEWER    CONSTRUCTION.  263 

structed,  and  keeping  a  daily  account  of  the  work  done  by 
each  gang. 

Two  pipe-layers  may  be  connected  with  each  gang  if  the 
trench  can  be  rapidly  excavated;  otherwise  two  or  more  gangs 
may  have  a  pair  of  pipe-layers  in  common,  who  lay  pipe  first 
in  one  trench  and  then  in  another,  as  sufficient  length  of  each 
is  excavated.  For  manholes,  flush-tanks,  and  other  masonry 
appurtenances  a  mason  and  two  helpers  may  work  together, 
passing  from  point  to  point  as  needed.  For  brick  sewers  two, 
four,  or  even  six  or  eight  masons  may  work  together,  the 
number  in  a  gang  usually  being  even.  The  number  of  masons' 
helpers  depends  somewhat  upon  the  depth  of  the  sewer,  one 
or  more  extra  ones  being  required  to  lower  brick  and  mortar 
if  the  depth  is  considerable.  For  a  depth  of  8  feet  or  less 
approximately  the  following  will  be  needed :  two  masons,  four 
helpers;  four  masons,  seven  helpers;  eight  masons,  fourteen 
helpers. 

Besides  the  teams  employed  in  hauling  material  to  the 
work  there  should  be  one  for  carrying  from  place  to  place 
mortar-boxes,  tool-boxes,  and  other  heavy  articles. 

It  is  difficult  to  say  anything  definite  concerning  the 
number  of  men  which  should  form  an  excavating-gang.  There 
should  be  sufficient  to  keep  the  pipe-layers  or  masons  con- 
stantly at  work.  Each  gang  or  set  of  gangs  to  which  a  pair 
of  pipe-layers  or  force  of  masons  is  assigned  should  be  just 
large  enough  to  open  and  back-fill  trench  at  the  average  rate 
at  which  the  sewer  is  laid.  If  the  sewer  frequently  varies  in 
depth  or  ease  of  digging  it  is  often  well  to  assign  a  force  of 
masons  or  pipe-layers  to  two  gangs,  always  endeavoring  to  so 
arrange  that  one  of  these  is  in  soil  rapidly  trenched  whenever 
the  other  is  in  deep  or  difficult  work.  For  8-foot  excavation 
in  good  soil  requiring  little  bracing  25  to  30  men  at  the  shovel 
is  usually  an  economical  number;  at  15  feet,  if  no  excavating- 
machinery  is  used,  60  to  80  will  be  required  for  equally  rapid 


264  SEWERAGE. 

work.  On  account  of  the  considerable  sheathing  necessary  at 
such  depths  and  for  other  reasons  it  may  be  better,  however, 
to  still  maintain  the  gang  at  25  or  30  men,  and  assign  the 
sewer-masons  or  -layers  to  two  gangs.  It  is  usually  undesir- 
able to  change  the  size  or  personnel  of  gangs  after  they  have 
once  been  gotten  into  good  working  shape. 

If  a  trench  runs  into  very  wet  soil  or  quick  or  running 
sand  gangs  as  large  as  the  above  cannot  be  used  to  advantage, 
since  not  only  must  sheathing  be  set  and  driven  right  up  to 
the  excavation  as  it  proceeds,  but  the  pipe  or  sub-drain  must 
be  laid  or  foundation  put  in  foot  by  foot  as  the  bottom  of  the 
trench  is  reached;  also  an  upheaval  of  the  quicksand  bottom, 
caving,  and  other  accidents  may  cause  occasional  stoppages  of 
the  work  for  a  few  minutes,  when  almost  the  entire  gang 
must  lie  idle  or  go  to  back-filling.  In  such  difficult  work  on 
pipe  sewers  a  gang  may  consist  of  a  foreman,  a  sheather,  two 
pipe-layers,  and  five  or  six  laborers.  If  the  ground  is  very 
wet  it  is  advisable  to  open  only  a  little  trench  at  a  time,  since 
the  more  that  is  open  below  water-level  the  greater  the 
amount  of  water  which  will  flow  through  the  trench  and  inter- 
fere with  the  work.  Under  such  circumstances  the  gangs 
should  be  small. 

If  the  back-filling  is  not  to  be  rammed  it  is  the  custom  of 
many  contractors  to  use  the  entire  gang  for  the  last  20  to  30 
minutes  each  day  in  back-filling.  This  arrangement  has  the 
advantage  of  not  requiring  an  extra  gang  and  foreman  for 
back-filling.  But  if  there  are  three  or  more  gangs  excavating 
it  would  perhaps  be  better  to  keep  one  gang  continually  back- 
filling. This  is  certainly  advisable  in  all  cases  where  the 
trench  is  to  be  thoroughly  tamped. 

The  contractor,  general  foreman,  or  timekeeper  should 
visit  each  gang  just  after  the  beginning  and  just  before  the 
ending  of  each  day's  work,  at  the  least,  to  learn  of  any 
material  needed  or  difficulty  encountered,  and  also  to  get  th? 


PRACTICAL   SEWER    CONSTRUCTION.  265 

"  time  "  of  the  men,  which  may  have  been  taken  by  the  fore- 
man, or  may  better  be  taken  directly  by  one  of  the  three 
above  mentioned. 

If  Italians  or  other  non-resident  workmen  be  employed 
(and  if  the  work  is  in  a  small  city  and  requires  many  men 
outside  labor  must  be  obtained)  they  are  usually  housed 
together  in  barns  or  empty  houses  or  shanties  constructed 
for  the  purpose  on  the  outskirts  of  the  city.  If  these  can  be 
located  near  a  stream  the  men  will  usually  take  advantage  of 
the  opportunity  to  wash  themselves  and  their  clothes  and  keep 
in  better  health  than  if  otherwise  situated.  The  necessity  for 
walking  a  long  distance  to  and  from  work  will  result  in 
decreased  energy  in  their  labor,  and  should  be  avoided.  It 
will  sometimes  pay  to  have  the  teams  carry  them  to  and  from 
the  work.  It  will  also  be  to  the  contractor's  advantage  to  see 
that  their  food  is  wholesome.  A  considerable  experience  with 
Italian  laborers  has  convinced  the  author  that  as  a  class  they 
are  more  appreciative  than  are  native  laborers  of  both  kind- 
ness and  harsh  treatment,  and  are  shrewd  readers  of  motives 
of  conduct.  If  justly  though  firmly  treated  they  are  polite, 
obedient,  and  good  workers,  slow  to  wrath,  but  dangerous  if 
ill  treated.  "  Sore-heads  "  among  them  should  be  gotten  rid 
of  at  once. 

Pay-days  should  come  at  as  long  intervals  as  possible, 
because  of  the  diminished  force  which  can  be  made  to  work 
for  the  following  day  or  two,  if  for  no  other  reason.  For  some 
reason  masons  seem  to  be  peculiarly  subject  to  the  failing  of 
"  pay-day  drunks,"  and  if  possible  an  arrangement  should  be 
made  with  them  to  pay  their  expenses  wherever  they  wish  to 
board  and  a  small  weekly  amount  of  pocket-money,  the 
balance  being  paid  them  when  their  work  is  completed. 
Monthly  payments  are  generally  made  to  the  laborers,  imme- 
diately after  the  payment  of  the  monthly  estimates. 


266  SEWERAGE. 

ART.   65.     TRENCHING  BY  HAND. 

The  line  of  the  trench  being  given  by  centre  stakes,  the 
sides  of  the  excavation  are  indicated  by  measuring  the  proper 
distance  on  each  side  of  the  stakes  and  stretching  sash-cord 
or  clothes-line  there  and  marking  the  ground  along  this  line 
by  means  of  a  pick.  The  laborers  are  then  placed  at  regular 
intervals  along  the  trench,  varying  from  6  to  20  feet,  in  single 
line  in  most  cases,  but  if  the  trench  is  8  feet  or  more  wide 
they  may  be  in  double  line.  It  may  be  well  to  define  in  some 
way,  as  by  a  mark  in  the  ground  or  stake  at  one  side  of  the 
trench,  equal  lengths  of  trench,  one  man  being  required  to 
work  within  the  limits  of  each  length.  Where  possible  it  is 
desirable  that  this  length  be  that  which  can  be  completed  in 
a  half  or  a  whole  day. 

If  the  street  is  macadamized  or  gravelled  or  has  a  hard  dirt 
surface  a  contractor's  "  rooter  plow  "  may  be  used  to  break 
the  surface;  but  this  is  not  advisable  in  narrow  trenches,  nor 
should  the  surface  be  broken  beyond  the  sides  of  the  trench, 
since  if  sound  it  helps  to  prevent  caving  of  the  sides. 

If  there  is  any  paving  material  on  the  street  it  should  be 
thrown  upon  one  side  of  the  trench,  and  the  remaining 
excavated  material  upon  the  other  side,  the  material  on  each 
side  being  kept  back  a  foot  or  two  from  the  edge  of  the  trench 
to  allow  a  pathway  for  foremen  and  inspector  and  for  lowering 
material,  but  still  more  to  prevent  excavated  material  from 
falling  back  into  the  trench.  Thus  one  side  of  the  street  is 
left  open  to  travel,  the  pile  of  paving  material  acting  as  a  guard 
to  the  trench  on  that  side.  If  so  much  soil  is  to  be  thrown 
out  or  the  street  is  so  narrow  that  it  cannot  all  be  placed  upon 
one  side  of  the  trench  it  may  be  placed  upon  both  sides,  the 
paving  material  being  kept  separate,  say  along  the  outside 
edge  of  one  bank;  but  it  would  be  better  to  use  trench- 
machinery  and  thus  avoid  blocking  the  street  entirely.  The 


PRACTICAL    SEWER    CONSTRUCTION.  267 

amount  which  can  be  placed  upon  one  side  of  the  street  with- 
out covering  the  sidewalk  may  be  increased  by  setting  there 
a  platform  and  guard,  as  shown  in  Fig.  n. 

The  first  earth  cast  out  should  be  thrown  to  what  will  be 
the  outside  edge  of  the  bank,  since  it  cannot  be  thrown  there 
when  the  trench  is  deeper  without  double  handling.  The 
gutters  should  be  kept  open  and  free  from  any  excavated 
material.  Down  to  a  depth  of  9  to  12  feet  the  earth  can  be 
cast  to  the  surface,  although  after  5  or  6  feet  is  reached  it  will 


FIG.  ii.— EXCAVATION-PLATFORM. 

be  necessary  to  keep  additional  men  on  the  surface  to  throw 
back  onto  the  pile  the  material  so  cast  out.  When  the  depth 
exceeds  9  to  12  feet  it  will  be  necessary  to  handle  the  material 
twice  before  it  reaches  the  surface,  by  placing  a  platform  or 
staging  about  6  or  7  feet  below  the  surface,  onto  which  the 
earth  is  thrown  by  two  to  four  men,  and  from  which  it  is 
thrown  to  the  surface  by  one  man.  If  the  depth  exceeds  16 
or  1 8  feet  still  another  platform  will  be  necessary  about  7  or 
8  feet  below  the  first.  These  platforms  are  usually  made  by 
resting  plank  upon  the  braces  or  rangers  of  the  sheathing. 
(Except  in  rock  cuts  there  are  almost  no  conditions  under 
which  a  trench  10  feet  or  more  in  depth  should  be  left 
unbraced.)  The  platform  may  consist  of  short  pieces  of  plank 
placed  crosswise  of  the  trench,  their  ends  resting  on  the 
rangers,  or  of  long  plank  lengthwise  of  the  trench  resting  upon 
the  braces.  The  latter  cannot  well  be  used  if  the  trench  is 


268 


SEWERAGE. 


less  than  5  feet  wide,  but  is  the  better  form  for  wide  trenches. 
If  there  is  more  than  one  tier  of  longitudinal  platforms  the 
successive  tiers  should  be  placed  alternately  upon  opposite 
sides  of  the  trench;  or  if  cross-platforms  are  used  the  right 
side  of  one  should  be  vertically  above  the  left  side  of  the  next 
lower,  alternate  platforms  being  vertically  above  each  other. 
The  number  of  men  excavating  which  cast  onto  one  platform 


rtitrrmmn 


m 


s 


lA-Vj 
FIG.  12. — CROSS-STAGING  IN  TRENCH. 

may  be  only  two,  but  should  increase  with  the  difficulty  of 
excavating,  so  as  to  keep  the  staging-man  busy. 

Where  it  is  allowed  (as  it  is  in  many  cities),  and  the  trench 
is  over  10  feet  deep,  it  is  often  economical,  except  in  hard 
rock,  dry  sand,  or  quicksand,  to  make  the  excavation  in  alter- 
nate tunnels  and  open  trenching,  the  sections  of  each  being  8 
to  20  feet  long.  The  tunnel  is  usually  made  about  5  feet 
high.  The  amount  of  material  to  be  removed  and  of  bracing 
to  be  put  in  is  thus  reduced.  But  tunnelling  should  never  be 
allowed  under  streets,  except  in  rock,  unless  the  tunnel  is 
afterwards  opened  and  back-filled  as  open  trench,  being  used 
only  to  save  bracing;  since  it  is  practically  impossible  to  so 
compact  the  back-filling  in  a  tunnel  as  to  prevent  future 
settlement,  which  may  not  occur,  however,  until  months  or 
years  later,  when  the  contractor  has  been  relieved  of  all 


PRACTICAL   SEWER    CONSTRUCTION.  269 

responsibility.  Where  the  amount  of  traffic  on  a  street  or 
other  conditions  require  it,  however,  a  tunnel  may  be  run 
under  the  street  and  a  masonry  lining,  which  may  be  the 
sewer  itself,  built  against  the  outside  of  the  excavation,  so 
that  there  is  no  back-filling  except  in  the  form  of  masonry; 
which  construction  requires  special  tunnelling-machinery  and 
methods.  In  Paris  by  the  use  of  a  shield  a  tunnel  19  feet 
outside  diameter  was  run  with  a  covering  in  some  places  of 
only  2  feet  between  it  and  the  street-paving  above,  without 
causing  any  cracks  in  the  latter.  A  considerable  number  of  cities 
in  this  country  have  built  sewers,  both  large  and  small,  in  earth 
and  rock  tunnels.  A  notable  instance  of  sewer-tunnelling  is  found 
in  the  sewers  tunnelled  through  sand-rock  at  St.  Paul,  Minn.,  the 
tunnel,  when  lined  on  the  bottom,  constituting  the  sewer.  Restric- 
tions against  tunnelling  should  not  of  course  apply  to  lines 
whose  depth  is  75  feet  or  more,  such  as  those  passing  through 
ridges. 

There  is  a  tendency,  if  a  right-handed  laborer  always  faces 
one  way  while  picking,  for  the  trench  to  work  to  his  left  as  it 
descends.  He  should  be  taught  to  avoid  this  by  keeping  his 
left  side  to  the  side  of  the  trench  at  which  he  is  picking,  so 
that  both  sides  shall  make  the  same  angle,  if  any,  with  the 
vertical. 

It  pays  to  keep  the  picks  sharpened  and  good  shovels  in 
the  men's  hands.  For  this  purpose  there  should  be  25  to  100 
per  cent  more  picks  than  laborers,  to  allow  opportunity  for 
sharpening  them.  For  digging,  the  round-pointed  shovel  is 
best,  but  staging-men  and  mortar-mixers  should  use  square- 
pointed  shovels.  There  should  be  a  few  extra  shovels  con- 
stantly on  hand,  including  a  few  long-handled  ones,  but  these 
latter  should  not  be  used  for  trenching  except  in  deep 
trenches  where  the  shovelling  is  very  easy. 

In  soil  where  caving  is  frequent  and  sheathing  is  not  used 
the  trench  should  be  refilled  as  soon  as  possible,  since  the 


270  SEWERAGE. 

longer  it  stands  the  greater  the  probability  of  caving.  Soils, 
such  as  clay  or  other  heavy  ground,  having  some  cohesion, 
will  usually  give  warning  of  caving  by  cracking  a  few  feet  back 
from  the  edge  of  the  trench,  and  should  be  braced  as  soon  as 
such  sign  appears.  Gravelly  soils  or  dry  sand  usually  give  no 
such  warning,  and  are  particularly  dangerous  on  this  account 
and  because  they  may  bury  and  suffocate  the  men;  while 
clay,  coming  in  lumps,  although  it  may  bury  and  even  crush 
them,  will  permit  them  to  breathe  until  they  can  be  rescued, 
Trenches  in  gravelly  and  sandy  soil  should  always  be  sheathed. 

If  a  boulder  is  met  with  it  may  be  raised  from  the  trench 
by  a  derrick  or,  if  too  large  for  this,  may  be  blasted.  Before 
blasting  the  earth  should  be  removed  from  all  sides  of  the 
boulder  and  the  trench  in  the  vicinity  should  be  braced.  It 
may  sometimes  be  cheaper  to  dig  a  hole  in  the  side  of  the 
bank  and  roll  the  boulder  into  this  out  of  the  way.  In  some 
cases,  when  the  sewer  would  pass  entirely  under  the  boulder, 
this  may  be  left  undisturbed  and  tunnelled  under.  If  it 
merely  protrudes  into  the  trench  a  portion  may  be  removed 
by  "  feathers  and  wedge  "  or  a  heavy  sledge. 

If  a  water-  or  gas-pipe  or  other  conduit  run  diagonally 
across  a  trench,  or  run  in  it,  or  cross  one  more  than  8  or  10 
feet  wide,  it  should  be  supported  in  position  before  the  earth 
is  removed  from  under  it.  This  can  be  done  by  placing 
across  the  trench  at  intervals  of  12  feet  sufficiently  strong 
timbers  or  old  rails,  and  suspending  the  conduit  from  these 
by  chains  drawn  tight  by  driving  wedges  between  them  and 
the  beams.  Rope  should  not  be  used  for  this  purpose,  as 
rain  causes  it  to  contract  or  break  in  the  attempt  to  do  so. 
If  such  a  pipe  lies  in  the  bank,  close  to  or  slightly  protruding 
into  the  trench,  the  bank  should  be  thoroughly  braced  just 
under  the  pipe  and  the  pipe  itself  be  held  in  place  by  braces. 
These  braces  should  not  be  removed  when  the  trench  is  back- 
filled; and  if  the  pipe  is  suspended  the  trench  should  be  filled 


PRACTICAL   SEWER    CONSTRUCTION.  271 

and  thoroughly  tamped  under  and  around  the  pipe  before  the 
chains  are  removed.  The  breaking  .of  a  water-main  in  or  near 
a  sewer-trench  is  one  of  the  most  disastrous  accidents  which 
can  happen  to  it.  Small  house-connection  pipes  crossing  the 
trench  are  apt  to  be  broken  by  workmen  climbing  over  them 
and  should  be  protected,  as  by  a  piece  of  plank  or  of  a 
2X4  placed  across  the  trench  just  above  such  pipe,  the 
ends  extending  6  inches  or  more  into  the  banks  for  support. 
In  all  cases  where  there  is  danger  from  water-pipe  such  and 
so  many  gates  should  be  temporarily  closed  that  the  closing 
of  only  one  more  will  entirely  shut  off  the  pressure  from,  the 
threatening  line  of  pipe,  and  a  wrench  be  kept  at  hand  for 
closing  this. 

If  a  drain  crosses  the  trench  the  pipe  should  be  removed 
and  saved,  and  a  trough  substituted  during  construction,  its 
•ends  supported  in  the  banks.  The  back-filling  should  be 
carefully  tamped  under  this  and  the  pipe  relaid  in  the  trough. 

At  the  first  sign  of  quicksand  the  best  of  close  sheathing 
should  be  at  once  put  in,  an  experienced  foreman  put  over 
this  work  and  the  best  men  placed  upon  it  (see  Art.  67). 

The  soil  where  a  trench  has  previously  been  dug,  although 
it  were  years  before,  is  more  liable  to  cave  than  that  which 
has  never  been  disturbed,  and  the  sewer-trench  should  be 
kept  several  feet  from  such  old  trench  if  possible. 

ART.  66.      EXCAVATING-MACHINERY. 

As  a  general  statement  it  may  be  said  that  it  does  not  pay 
to  use  any  kind  of  machinery  in  excavating  where  the  trench 
is  less  than  8  or  9  feet  deep  or  wide,  although  it  may  be  desirable 
or  necessary  to  do  so  where  for  some  reason  the  excavated 
material  cannot  be  piled  along  the  side  of  the  trench.  The 
advantages  attending  the  use  of  earth-handling  machinery  are: 
greater  amount  of  material  excavated  with  a  given  number  of 


272  SEWERAGE. 

men,  less  danger  of  caving  of  banks  from  the  weight  of  earth 
piled  upon  them,  less  obstruction  to  street  traffic,  the  con- 
venience of  having  at  hand  means  for  raising  boulders,  lower- 
ing heavy  pipes,  or  other  material.  Each  of  these  advantages 
increases  in  force  with  the  depth  of  the  sewer.  With  several 
of  the  machines  now  on  the  market  the  cost  of  handling 
material  increases  but  little  with  the  depth.  The  machinery 
in  use  varies  from  an  ordinary  boom-derrick  to  an  elaborate 
system  of  trestles,  wire  ropes,  and  buckets,  which  may  stretch 
along  400  feet  or  more  of  trench. 

For  a  large  brick  sewer  a  handy  arrangement  is  that  of  two 
derricks  with  booms  about  40  feet  long,  both  placed  on  the 
same  side  of  the  trench  and  about  75  feet  apart.  Both  boom- 
and  main-falls  should  wind  upon  drums  driven  by  steam- 
power.  With  this  arrangement  a  bucket  of  earth  can  be 
hoisted  from  the  excavation  and,  passing  from  one  derrick  to 
another,  be  deposited  in  the  trench  125  or  even  145  feet 
away.  This  plan  is  not  adapted  to  narrow  trenches  nor  to 
those  where  any  considerable  length  of  trench  is  to  be  under 
excavation  at  one  time.  For  these  one  of  the  trestle-machines 
or  cable-ways  is  preferable,  the  former  more  particularly  for 
trenches  up  to  10  or  12  feet  in  width,  the  latter  for  wider 
ones  and  for  particular  cases,  such  as  crossings  of  railroad- 
tracks. 

The  cable-way  consists  essentially  of  a  wire  cable  sus- 
pended over  the  centre  of  the  trench,  on  which  run  one  or 
more  travellers  carrying  buckets;  the  earth  being  excavated 
at  one  point  and  cast  into  the  buckets,  which  are  raised  and 
carried  to  the  other  end  of  the  cable,  where  they  dump  thr 
earth  upon  the  completed  sewer.  It  is  essential  to  the  safety 
of  the  laborers  that  the  cable  be  most  substantially  anchored 
at  the  ends,  and  that  it  be  amply  strong  to  carry  any  load 
which  can  possibly  come  upon  it.  The  anchorage  is  usually 
in  the  shape  of  a  "  dead-man,"  but  the  ordinary  log  placed 


PRACTICAL    SEWER    CONSTRUCTION.  273 

in  the  trench  and  covered  with  earth  back-filling  should  not 
be  relied  upon.  Rock  may  be  piled  in  front  of  and  over  the 
log,  but  a  better  plan  is  to  bury  in  the  trench  a  platform  of 
stout  timber,  inclined  backward  about  45°  from  the  vertical, 
to  which  the  cable  is  fastened.  The  hoisting-  and  conveying- 
ropes  are  driven  by  an  engine  located  at  one  end  of  the  cable. 
Like  derricks,  the  cable-way  is  not  adapted  to  trenches  which 
move  forward  rapidly,  as  the  moving  and  resetting  of  it  take 
considerable  time  and  labor. 

In  the  trestle-machine  used  for  narrow  trenches  the  buckets 
travel  suspended  from  an  overhead  track  which  is  supported  at 
intervals  by  trestles  spanning  the  trench.  Generally  from  6  to 
20  buckets  are  in  use  at  once,  one  half  of  which  are  being  filled 
while  the  remainder  are  being  carried  to  the  dump  and  emptied. 
In  some  machines  the  track  forms  a  long  loop,  one  side  of  which 
is  for  going  and  the  other  for  returning  buckets.  There  are  then 
three  sets  of  buckets,  one  going  to  the  dump,  one  returning, 
and  one  set  being  filled.  For  wider  trenches  the  buckets  are 
generally  made  larger,  holding  from  J  to  i  cubic  yard  each,  and 
are  carried  upon  a  car  or  traveller  which  runs  back  and  forth  on 
an  overhead  track  supported  by  the  trestle.  To  obtain  the 
greatest  efficiency  of  the  machine  the  number  of  men  casting 
into  each  bucket  should  be  just  sufficient  to  fill  it  during  the 
time  occupied  in  removing,  emptying,  and  returning  a  set  of 
buckets. 

Such  machinery  is  economical  when  the  cost  of  running — 
including  all  labor  but  that  of  the  men  digging  in  the  trench 
— and  of  repairs,  plus  the  rental  or  interest  on  first  cost  of  the 
machine,  is  less  than  the  cost  of  "  staging  "  it  out  (as  the  use 
of  platforms  is  called)  plus  that  of  back-filling.  If  the  back- 
filling is  to  be  hand-tamped  this  last  item  should  not  be  in- 
cluded, since  if  a  machine  is  used  the  material  must  be  spread 
after  dumping.  A  good  trench-machine  is  usually  economical 


274  SEWERAGE 

when  either  depth  or  breadth  of  trench  exceeds  8  to  IO  feet 
in  ground  capable  of  rapid  trenching;  but  this  economical 
least  dimension  increases  with  the  decrease  in  the  rapidity  of 
excavation  possible.  Where  for  some  reason  the  excavation 
can  proceed  but  slowly  the  use  of  machinery  is  not  advisable 
for  economical,  though  it  may  be  for  other,  reasons. 

"Whatever  the  machinery  employed  it  should  work  suc- 
cessfully although  the  sheathing  extend  at  least  6  feet  above 
the  surface  along  each  side  of  the  trench,  should  be  able  to 
drop  a  bucket  anywhere  in  the  trench,  each  bucket  being 
always  under  perfect  control,  and  no  cable  or  rope  should 
hang  within  6  feet  of  the  ground.  It  is  better  that  it  should 
have  no  cross-ties  or  other  parts  extending  across  the  trench 
within  6  feet  of  the  ground,  and  that  it  should  not  obstruct 
the  street  for  more  than  2  feet  on  each  side  of  the  trench. 

For  deep  trenching  through  city  streets  the  use  of  trench 
machinery  is  strongly  recommended  as  of  advantage  to  both 
city  and  contractor. 

Most  makes  of  trench  machinery  can  be  either  rented  or 
bought.  For  a  village  or  small  city  the  former  is  generally 
preferable  if  the  work  on  which  it  is  to  be  used  can  be  pushed. 
But  if  it  will  be  needed  for  more  than  one  season  it  may  be 
preferable  to  buy  instead. 

The  machines  above  referred  to  are  for  raising  the  dirt  and 
transporting  it  to  the  rear  or  dumping  it  into  wagons.  There  are 
other  machines,  however,  for  doing  the  actual  work  of  excavation. 
Of  these  there  are  at  least  two  general  styles  upon  the  market, 
one  working  on  the  general  principle  of  the  ladder  dredge,  the 
other  a  wheel  carrying  upon  its  periphery  a  number  of  buckets 
provided  with  cutting  teeth  or  edges  similar  to  the  bucket  of  a 
steam  shovel.  Both  ladder  and  wheel  can  be  raised  or  lowered 
by  the  operator  at  will  so  as  to  give  the.  required  depth  of  trench, 
and  have  been  used  for  excavating  trenches  up  to  20  feet  in  depth. 


PRACTICAL    SEWER    CONSTRUCTION.  275 

It  is  necessary  in  these  to  keep  the  track  well  adjusted  so  that 
the  ladder  arm  or  wheel  should  move  in  a  vertical  plane.  For 
cutting  in  prairie  soil,  clay,  or  other  material  which  will  stand  to 
full  depth  for  an  hour  or  two  without  bracing,  and  which  does  not 
contain  boulders,  "nigger-heads,"  hard  pan  or  other  material 
of  a  similar  nature,  these  machines  have  been  used  in  a  great 
many  cases  to  the  advantage  of  the  contractor.  The  conditions 
under  which  they  can  be  used  advantageously,  however,  are  more 
limited  than  with  the  ordinary  trench-machinery.  Neither  of 
these  classes  of  excavating  machines  transport  the  material,  but 
they  dump  it  either  in  piles  along  the  side  of  the  trench  or  into 
carts. 


ART.  67.     SHEATHING. 

Just  when  a  trench  can  be  relied  upon  to  stand  without 
sheathing  and  when  it  cannot  is  something  that  only  experi- 
ence can  teach.  Sheathing  is  expensive,  but  not  so  expensive 
as  excavating  a  trench  which  has  begun  to  cave,  to  say  noth- 
ing of  settling  for  injuries  and  death  of  laborersc  If  earth  has 
been  piled  upon  a  bank  which  afterwards  caves  it  may  be 
necessary  to  re-excavate  more  material  than  all  that  which 
would  have  been  excavated  had  no  caving,  occurred,  and  all 
of  this  must  be  removed  to  some  distance  because  there  is  no 
bank  upon  which  to  pile  it.  Not  only  that,  but  the  soil  is 
liable  to  continue  to  slide  into  the  trench,  making  it  almost 
impossible  to  keep  the  bottom  uncovered.  If,  after  caving 
has  begun,  sheathing  is  used  the  difficulty  of  placing  it  is 
greatly  increased.  A  trench  which  if  sheathed  would  have 
given  no  trouble  may  become  a  most  discouraging  hole  into 
which  many  times  the  cost  of  sheathing  must  be  placed  in  the 
form  of  labor  before  the  sewer  is  built  therein.  The  author's 


276  SEWERAGE. 

experience  has  been  that  it  does  not  pay  to  take  many 
chances  with  unsheathed  trenches.  He  would  use  at  least 
skeleton  sheathing  in  every  trench  more  than  8  or  10  feet 
deep,  in  any  trench  in  gravelly  and  sandy  soil,  and  whenever 
the  least  sign  of  caving  appears.  Wherever  the  street  is  paved, 
if  sheathing  be  not  employed  a  plank  should  be  placed 
horizontally  on  each  side  of  the  trench  about  6  inches  below 
the  surface,  and  braces  driven  between  these  not  more  than 
6  feet  apart. 

Sheathing  is  usually  placed  as  follows:  A  plank  (a,  Fig. 
13)  is  placed  upright  in  the  trench  against  the  bank,  another 
(b)  12  feet  from  this,  and  two  against  the  other  bank  and 
directly  opposite  these.  Against  each  two  and  near  the 
street-surface  is  placed  a  horizontal  ranger  (cd  and  ef),  both 
at  the  same  level,  and  between  them  at  each  end  a  brace  is 
driven,  long  enough  to  be  a  tight  fit.  Two  other  rangers  (gk 
and  £/)  are  placed,  one  on  each  side  of  the  trench,  from  4  to 
6  feet  below  the  others,  and  braced.  Sometimes  these  lower 
rangers  are  placed  first.  The  ends  of  the  rangers  come  in  the 
middle  of  the  uprights,  the  braces  only  an  inch  or  two  from 
the  ends  of  the  rangers.  The  next  set  of  rangers  abut  against 
these  and  are  braced  in  the  same  way.  Generally  an  addi- 
tional upright  and  braces  are  placed  midway  of  each  ranger, 
This  forms  skeleton  sheathing. 

If  the  sheathing  is  to  be  close,  plank  are  slipped  behind 
the  rangers  and  in  contact  with  each  other,  and  one  or  more 
additional  braces  are  placed  at  equal  intervals  along  each  pair 
of  rangers.  For  bracing  only,  the  rangers  and  braces  are  used 
without  any  vertical  sheathing.  These  are  ordinarily  placed 
a  foot  or  two  from  the  surface,  or  just  beneath  and  in 
front  of  an  exposed  water-main  or  other  conduit.  When  a 
series  of  rangers  and  braces  are  placed  one  just  below  the 
other  horizontal  sheathing  is  formed. 

As  the  trench  is  deepened  the  sheathing  should  be  driven 
so  that  its  lower  end  is  as  near  as  possible  to  the  bottom  of 


PRACTICAL    SEWER    CONSTRUCTION. 


277 


the  trench,  unless  rock  or  some  firm  soil  be  previously 
reached.  In  quicksand  or  running  sand  the  bottom  of  the 
sheathing  should  always  be  kept  at  least  one  foot  below  the 
bottom  of  the  excavation.  This  is  essential  if  the  work  is  to 
be  done  without  considerable  loss  of  money  and  perhaps  of 
life.  As  many  men  as  are  necessary  to  insure  this  should  be 
kept  constantly  at  work  driving  the  sheathing.  No  two  planks 
behind  the  same  ranger  should  be  driven  at  once,  as  the  latter 
would  in  that  case  be  apt  to  follow  them  down,  which  it 
should  not  do. 

If  there  is  a  tendency  for  the  sheathing  to  be  forced  in  at 


FIG.  13. — SKELETON  SHEATHING. 

the  bottom  by  the  bank,  as  in  the  case  of  quick  or  running 
sand,  a  set  of  rangers  and  braces  should  be  put  in  place  im- 
mediately under  the  lowest  set  already  in  position  as  soon  as 
the  excavation  is  low  enough  to  permit  it.  As  the  excavation 
and  sheathing  are  carried  down  this  last  set  of  rangers  should 
be  driven  down,  always  being  kept  level  crosswise  of  the 
trench  and  just  above  its  bottom,  until  it  is  the  proper  dis- 
tance below  the  preceding  set,  when  it  is  driven  no  further, 
but  another  set  is  started  under  it.  If  the  bank  is  tolerably 
stable  the  stiffness  of  the  sheathing-plank  can  be  relied  upon 
to  keep  it  in  place  below  the  second  ranger  until  the  trench 


278  SEWERAGE. 

is  sufficiently  deep  to  permit  placing  the  third  ranger  in  its 
proper  position  without  any  further  driving. 

Each  brace  should  be  exactly  beneath  the  braces  in  the 
tiers  above. 

There  is  considerable  friction  between  the  sheathing  and 
the  bank  on  one  side  and  rangers  on  the  other,  and  after  two 
sets  of  rangers  are  in,  the  driving  becomes  quite  difficult  and 
the  upper  ends  of  the  plank  become  battered  and  broomed 
and  the  plank  broken,  sometimes  even  when  they  are  pro- 
tected by  caps.  Ordinarily  10  or  12  feet  is  the  greatest  depth 
to  which  plank  can  be  driven  economically.  It  then  becomes 
necessary  to  start  a  new  course  of  sheathing,  which  is  placed 
inside  the  upper  course,  its  back  resting  against  the  rangers 
of  this.  The  second  course  is  driven  and  held  in  place  by 
rangers  and  braces  as  was  the  other,  and  may  be  succeeded 
by  one  or  more  other  courses  each  10  or  12  feet  high.  When 
a  new  course  of  sheathing  is  started  it  is  advisable  to  tem- 
porarily fasten  planks  horizontally  in  front  of  and  behind  this 
sheathing  near  the  top,  by  a  nail  at  each  end  driven  into  a 
sheathing-plank,  to  keep  the  plank  in  line  and  steady  them 
while  driving. 

In  placing  each  course  after  the  first  one  an  opening  must 
be  left  at  each  vertical  line  of  braces,  since  the  sheathing 
cannot  be  driven  there.  If  these  openings  give  trouble  they 
may  be  closed  by  slipping  into  them,  behind  the  rangers, 
5 -foot  lengths  of  plank  when  the  trench  has  reached  that  dis- 
tance below  the  first  course  of  sheathing,  and  driving  these 
to  keep  pace  with  the  other  sheathing.  When  the  trench  is 
5  feet  deeper  still  another  5 -foot  length  of  plank  may  be 
slipped  behind  the  ranger  on  top  of  the  former  length,  and 
so  on.  A  short  piece  of  plank,  at  least,  should  be  kept  in 
the  bottom  of  this  opening  to  keep  the  planks  on  either  side 
the  proper  distance  apart. 

Another  method  of  closing  these  openings  is  to  cut  a  plank 
just  long  enough  to  reach  from  the  bottom  of  one  ranger  to 


PRACTICAL    SEWER    CONSTRUCTION. 


279 


the  top  of  the  next  and  a  little  wider  than  the  opening. 
This  is  placed  over  the  opening  against  the  face  of  the  sheath- 
ing, and  between  the  rangers,  to  which  blocks  are  nailed  to 
hold  it  in  this  position  (see  Fig.  14). 

In  some  cases  it  will  not  do  to  leave  this  space  open  for 
even  a  foot  above  the  bottom  of  the  trench,  as  in  quicksand. 
It  may  then  be  advisable  to  use  a  somewhat  different  system 
of  rangers,  as  follows:  In  placing  rangers  for  the  first  course 
of  sheathing,  where  one  ranger  is  ordinarily  placed  two  will 
be  placed,  one  in  front  of  the  other  but  separated  from  it  by 
a  small  piece  of  plank  at  the  end  of  each  brace.  The  front 
ranger  may  be  but  a  2-inch  plank.  The  second  course  of 


FIG.  14. — SHEATHING  UNDER  BRACES. 

sheathing  is  slipped  between  the  two  rangers  and  when  it  is 
all  in  place  except  where  the  spacing-blocks  interfere  th^ 
braces  are  driven  along  about  a  foot,  the  spacing-blocks 
knocked  out,  and  sheathing  dropped  into  the  spaces  they 
occupied.  Generally  plank  behind  a  brace  cannot  be  driven, 
owing-  to  the  friction,  but  when  the  one  next  to  it  has  been 
driven  the  brace  can  be  moved  over  in  front  of  this  and  the 
former  then  driven. 

Where  there  is  more  than  one  course  of  sheathing,  or 
whenever  the  bottom  of  any  course  is  not  kept  at  the  bottom 
of  the  trench,  all  braces  in  each  vertical  line  should  be  tied 
together  by  diagonal  bracing  of  planks  nailed  to  them;  otherwise 
one  side  of  the  sheathing  may  drop,  loosening  the  braces  and 
causing  a  complete  collapse  of-  sheathing  and  trench.  The 


280  SEWERAGE. 

author  has  seen  several  serious  accidents  due  to  the  neglect  to 
use  such  diagonal  bracing. 

The  sheathing  is  usually  of  hemlock  plank,  although  pine 
would  be  better,  being  less  brittle.  Maple  and  other  hard 
wood  has  been  used  in  a  few  instances.  The  plank  is  usually 
2  inches  thick,  although  heavier  may  be  advisable  in  deep, 
wide  trenches  or  where  it  is  desirable  to  use  as  few  rangers 
and  braces  as  possible.  It  should  never  be  less  than  2  inches 
thick.  Ten  or  12  feet  is  the  usual  length,  although  18  or  more 
is  sometimes  used.  But  the  great  amount  of  friction  between 
such  long  plank  and  the  earth  makes  it  extremely  difficult  to 
drive  the  last  6  or  8  feet,  the  top  of  the  plank  being  usually 
broomed  or  broken  in  the  attempt.  For  the  same  reason  the 
width  of  the  plank  does  not  usually  exceed  6  or  8  inches. 
All  the  sheathing  in  a  given  course  should  be  of  approxi- 
mately the  same  length.  Sheathing-plank  should  be  sharp- 
ened to  a  chisel  edge,  the  flat  side  being  placed  against  the 
bank,  and  the  edge  which  will  not  be  in  contact  with  the 
plank  last  driven  should  be  bevelled,  that  the  plank  may  hug 
the  bank  and  keep  a  close  joint  with  the  one  previously 
driven.  The  bevel  may  be  3  to  5  inches  long.  The  top  of 
the  sheathing-plank  should  be  bevelled  on  each  edge,  to 
lessen  splitting  and  binding  and  to  permit  of  using  a  driving- 
cap,  which  is  advisable  if  the  sheathing  drives  hard,  to  keep 
the  plank  from  brooming. 

For  driving  the  sheathing  a  hardwood  maul  is  ordinarily 


FIG.  15.— DRIVING-CAP  AND  MAUL. 

used,  about  6  inches  in  diameter  and  15  inches  long,  with  a 
wrought-iron  hoop  banding  each  end. 


PRACTICAL   SEWER    CONSTRUCTION. 


281 


If  a  large  amount  of  sheathing  is  to  be  driven  in  deep 
trenches  a  steam-hammer  pile-driver  may  be  used  to  advan- 
tage. This  does  not  broom  the  pile,  and  by  using  it  sheath- 
ing 1 8  feet  long  or  more  may  be  driven.  It  is  particularly 
applicable  to  sand  and  elastic  soils. 

If  the  ground  is  such  as  to  require  sheathing  from   the* 


Verticol  Sheathing 
Started.       a  * 

FIG.  16. — HORIZONTAL  SHEATHING. 

very  beginning  of  the  excavation  it  would  be  difficult  to  keep 
vertical  sheathing  standing  and  in  line  while  the  trench  is  only 
I  to  3  feet  deep,  and  it  would  greatly  interfere  with  casting 
out  the  excavated  material.  It  will  be  better  in  such  a 
case  to  erect  skeleton  sheathing,  with  only  one  set  of  rangers 
and  braces  and  short  uprights,  behind  the  uprights  placing 
plank  laid  horizontally.  When  this  construction  has  been 
carried  down  5  or  6  feet  vertical  sheathing  can  be.  started 
and  continued  as  above.  But  even  then  if  the  vertical 
sheathing  is  more  than  8  feet  long  it  will  be  necessary  to  use 
platforms  or  staging,  unless  a  sheathing-plank  can  be  omitted 
every  5  or  6  feet  and  the  earth  cast  out  through  the  open- 
ing thus  left.  On  account  of  the  difficulties  just  described  it 
is  better,  if  the  trench  is  so  deep  as  to  require  more  than 
one  course  of  sheathing,  to  place  shorter  sheathing  in  the  top 
course — for  instance,  6-foot  sheathing  and  then  12-foot  in  a 
15-  to  1 8-foot  trench. 

Some  contractors  use  horizontal  sheathing  altogether,  the 
verticals  being  only  3  or  4  feet  long,  several  being  placed  one 


282  SEWERAGE. 

above    the    other.       Most    American    contractors,    however, 
prefer  the  vertical  sheathing. 

The  size  of  the  rangers  may  vary  between  wide  limits,  but 
in  any  one  trench  they  should  all  be  the  same  length,  and 
when  in  position  the  ends  of  all  should  come  opposite  or 
under  each  other.  Two-inch  plank  may  be  used  for  rangers  in 
ordinary  loamy  or  clayey  soil  and  shallow  trenches,  and  the 
braces  placed  with  sufficient  frequency  to  prevent  their  belly- 
ing too  much.  This  would  in  many  cases  bring  the  braces  so 
close  to  each  other  as  to  interfere  with  the  work,  and  it  will 
then  be  advisable  to  use  4X4  or  4X6  material.  The 
author  prefers  these  in  any  case,  as  being  stronger,  but  neither 
costing  nor  weighing  more,  than  2-inch  plank.  If  excavating- 
machinery  is  used  the  braces  should  be  at  least  5  or  6  feet 
apart,  and  the  rangers  of  4  X  6  or  6  X  8  timber.  The 
deeper  the  trench  the  heavier  should  be  the  rangers  and 
braces. 

The  braces  should  be  heavier  also  the  wider  the  trench, 
since  they  must  act  as  posts.  They  are  often,  for  conve- 
nience, made  of  the  same  size  of  timber  as  that  used  for 
rangers.  Each  brace  must  be  fitted  to  its  place,  since  the 
width  of  a  trench  usually  varies  at  different  points  within  a 
range  of  several  inches.  For  rinding  the  length  of  brace 


FIG.  17. — SLIDING  ROD  FOR  MEASURING  BRACKS. 

required  it  is  handier  to  use  a  sliding  rod  than  a  measuring- 
rule.  The  brace  should  be  made  a  little  longer  than  the  dis- 
tance between  rangers,  that  it  may  drive  hard  into  place  and 
n't  there  tightly.  To  make  this  driving  easier  one  edge  of 
one  end  of  the  brace  may  be  slightly  bevelled. 

Instead  of  wooden  braces  extensible  iron  ones  are  in  quite 
general  use,  and  for  narrow  trenches  at  least  are  equally  as  good 
and  much  more  convenient,  since  they  can  be  quickly  adjusted 
to  any  position  and  used  over  and  over  again.  For  wide  trenches 


PRACTICAL    SEWER    CONSTRUCTION.  283 

those  in  the  market  are  hardly  stiff  enough,  but  are  apt  to  buckle 
under  extreme  pressure.  However,  trussed  beams  with  extensible 
ends  can  be  used,  which  meet  this  objection.  If  much  bracing 
is  to  be  done  the  cost  of  extensible  braces  can  be  saved  in  the 
carpenters'  wages  many  times  over. 

Much  heavier  sheathing  than  here  described  may  be 
necessary  in  deep  trenches  in  some  soils.  In  stiff  marsh  land 
near  New  York  City,  in  a  trench  26  feet  wide  and  25  feet  deep, 
6-inch  sheathing  was  found  necessary,  with  10  X  10  rangers 
and  8X8  braces  5  feet  apart  horizontally  and  vertically. 

For  deep  work  or  other  conditions  calling  for  unusual  strength 
in  the  sheathing,  steel  piles  have  been  used,  a  great  many  designs 
of  which  have  been  placed  upon  the  market  since  about  1905. 
Most  of  these  are  comparatively  water  tight,  they  can  be  driven 
through  a  hard  soil  where  wooden  sheathing  could  not  be,  and 
they  are  stronger  than  most  wooden  sheathing.  Their  principal 
advantage  is  water-tightness,  and  they  are  especially  adapted  to 
sheathing  in  wet  soil  or  the  constructon  of  coffer-dams  in  trench- 
ing across  streams  or  other  bodies  of  water.  They  should  in 
most  instances  be  driven  with  a  driving  cap,  otherwise  their 
upper  ends  will  be  badly  battered  where  the  driving  is  hard. 
If  not  so  battered,  they  can  generally  be  drawn  and  used  again 
many  times.  It  is  generally  necessary  to  drive  these  by  machinery 
of  some  kind,  either  a  regular  pile  driver,  a  steam-hammer  pile 
driver  or  some  equally  powerful  device.  The  engine  of  a  pile 
driver  or  a  derrick  is  usually  required  to  draw  this  sheathing. 
The  steel  sheathing,  or  course,  is  much  more  expensive  in  first 
cost  than  wooden  sheathing,  requires  machinery  for  driving,  which 
wooden  sheathing  generally  does  not,  and  so  is  adapted  only  to 
work  of  considerable  magnitude. 

In  cases  where  the  soil  was  soft  round  piles  have  been 
driven  a  few  feet  apart  along  the  side  lines  of  the  trench  before 
excavation,  and  as  this  proceeded  horizontal  sheathing  was 
inserted  behind  the  piles  and  braces  placed  across  the  trench 
between  them. 


284  SEWERAGE. 

The  rangers  and  braces  can  be  used  over  and  over  again  if 
they  are  not  left  in  the  trench;  the  sheathing,  too,  can 
ordinarily  be  used  several  times;  but  each  time  a  set  is  used 
a  few  plank  will  probably  be  broken,  either  in  driving  or  in 
drawing.  As  stated  in  connection  with  Table  No.  21,  good 
sheathing  can  ordinarily  be  used  two  to  five  times,  taking  an 
average  of  all  used  at  the  outset. 

In  many  instances  it  is  desirable  to  leave  the  sheathing 
in  the  trench,  sometimes  with  and  sometimes  without  the 
rangers  and  braces.  The  conditions  calling  for  leaving  in 
sheathing  are :  that  drawing  it  may  endanger  the  sewer,  or 
water-  or  gas-pipes  in  the  street  near  the  trench,  or  adjacent 
buildings,  or  that  the  street-paving  will  be  injured  thereby. 
The  danger  to  buildings  usually  exists  only  in  connection  with 
deep  trenches  in  unstable  soil  or  where  a  building  is  quite 
near  a  sewer  which  lies  below  its  foundation.  Water-  or  gas- 
mains  would  be  endangered  if  within  two  or  three  feet  of,  and 
more  than  that  distance  above  the  bottom  of,  a  sewer-trench 
in  fairly  good  soil.  If  the  soil  has  shown  a  tendency  to  crack 
along  the  banks  near  the  trench  the  sheathing  should  not  be 
drawn  if  the  street  is  well  paved ;  and  if  water-  or  gas-pipe  or 
other  sewers  are  laid  in  such  street  the  judgment  of  the 
engineer  must  decide  at  what  distance  they  may  be  consid- 
ered safe  from  disturbance  if  the  sheathing  be  drawn.  If  the 
sheathing  has  been  driven  below  the  centre  of  a  sewer,  as 
must  be  done  under  some  conditions,  its  removal  would  dis- 
turb the  foundation  of  the  sewer  and  should  not  be  attempted. 
But  if  two  or  more  courses  of  sheathing  have  been  driven 
all  but  the  lowest  course  may  be  removed  if  the  sewer  only 
is  affected.  The  rangers  and  braces  as  well  as  the  plank  should 
usually  be  left  in.  If  the  banks  are  liable  to  cave  with  the 
drawing  of  the  sheathing  the  trench  should  be  filled  to  a  dis- 
tance above  the  sewer  at  least  equal  to  its  width  before  the  top 
braces  are  knocked  out  or  any  sheathing-plank  is  entirely  drawn* 


PR  A  C  TIC  A  L   SE  WER    CONS  TR  UC  TION. 


285 


Before  drawing  sheathing  the  back-filling,  if  it  is  not  to  be 
rammed,  should  be  carried  to  a  point  at  least  3  feet  above 
the  bottom  of  the  plank.  The  bottom  set  of  braces  and 
rangers  may  then  be  removed.  If  this  gives  less  than  2  feet  of 
back-filling  above  the  top  of  the  sewer  this  amount  should  be 
thrown  in  and  properly  tamped.  When  the  sewer  is  properly 
covered  the  remaining  braces  and  rangers  may  be  removed 
and  the  sheathing  entirely  drawn.  If  the  bank  should  cave 
badly  on  the  removal  of  the  braces  it  might  break  the  sheath- 
ing, and  in  such  a  case  it  may  be  better  to  continue  back- 
filling and  slowly  drawing  the  sheathing,  each  set  of  rangers 
being  removed  only  as  the  back-filling  reaches  them.  If  there 
is  more  than  one  course  of  sheathing  this  plan  should  be  fol- 
lowed in  every  case  with  all  but  the  top  course,  unless  the 
others  are  to  be  left  in  the  trench,  which  may  be  cheaper  in 
some  cases. 

Drawing  the  sheathing  is  often  a  difficult  matter  if  only 
the  hands  or  a  pick  be  used.  A  convenient  plan  is  to  use  a 
sheathing-puller,  made  of  iron  i£  or  2  inches  thick  and  3  or 


FIG.  18. — SHEATHING-PULLER 


4  inches  wide.  The  ring  on  the  clamp  should  be  so  placed 
that  the  clamp  will  slide  down  the  sheathing  when  not  sup- 
ported, remaining  constantly  horizontal.  After  placing  this 
in  position  on  a  horse  a  simple  pump-handle  motion  with 
the  lever  will  suffice  to  draw  the  plank.  A  chain  to  be 
hooked  tightly  around  a  sheathing-plank  may  be  used  as  a 
substitute  for  the  clamp,  but  is  not  convenient  for  close 


OF   THE 

UNIVERSITY 

OF 


286  SEWERAGE. 

sheathing,  which  must  be  pried  apart  to  admit  it.  Better 
than  this  sheathing  puller,  where  excavating-machinery  is 
being  used,  is  to  use  the  engine-power  to  draw  the  sheath- 
ing by  fastening  the  clamp  to  a  hoisting-rope. 

Where  a  building  is  so  situated  with  reference  to  the 
sewer-trench  that  its  stability  is  endangered  thereby  the 
greatest  care  should  be  taken  with  the  sheathing  to  prevent 
any  material  behind  it  from  caving  into  or  in  any  way  enter- 
ing the  trench.  To  insure  this  the  sheathing-plank  must 
be  tight  together — in  sand  it  may  be  necessary  to  use  tongued 
and  grooved  plank — and  their  bottoms  should  be  kept  well 
below  the  bottom  of  the  trench.  If  this  is  done  and  the 
bracing  is  strong  and  stiff  there  should  be  little  danger,  unless 
the  material  is  semi-fluid,  when  it  may  be  impossible  to  pre- 
vent a  settlement  of  the  ground  and  buildings,  unless  by 
freezing  the  soil  by  the  Poetsch  process  (an  exceedingly 
expensive  one)  or  some  similar  method. 

If  a  settlement  of  a  portion  of  a  building-foundation  seems 
probable  the  building  should  be  shored  and  jacked  up.  One 
method  of  accomplishing  this  is  to  make  openings  just  above 
the  ground-surface  6  to  10  feet  apart  and  of  a  size  to  permit 
large  beams — 10  X  12,  or  12  X  14  or  18 — to  be  passed  through 
them.  These  beams  are  supported  at  each  end  by  jacks, 
which  in  turn  rest  upon  blocking  placed  upon  the  ground.  A 
careful  watch  is  kept  of  these  and  at  the  least  sign  of  settle- 
ment of  the  ground  the  jack  above  is  screwed  up  an  amount 
equal  to  this  settlement.  As  a  further  precaution  it  may  be 
advisable  to  shore  up  the  walls  by  a  sufficient  number  of  heavy 
timbers,  whose  lower  ends  are  supported  upon  platforms  or 
grillage,  wedges  being  placed  under  the  foot  of  each  and 
driven  up  when  necessary  to  make  up  any  settlement  of  the 
ground.  The  shores  at  their  upper  ends  bear  against  beams 
bolted  to  the  walls  of  the  building,  or  in  masonry  walls  are 
received  by  openings  about  a  foot  deep  cut  therein.  Shores 


PRACTICAL   SEWER    CONSTRUCTION.  287 

alone  are  often  employed  when  the  building  is  not  valuable 
or  the  danger  is  small. 

ART.   68.     LAYING  SEWER-PIPE. 

It  will  save  considerable  trouble  in  the  laying  of  pipe  if 
the  foreman  has  the  trench  dug  exactly  to  line  and  grade  as 
ascertained  by  measuring  and  plumbing  from  a  grade-line 
already  set.  It  is  better  to  have  the  bottom  a  little  too  high 
rather  than  too  low. 

Pipe  sewer  is  usually  laid  up  the  grade,  and  the  pipes  are 
so  manufactured  that  the  specials  must  be  laid  with  their  bell 
ends  pointing  up.  Laying  the  sewer-pipe  in  this  way  is  more 
likely  to  produce  good  joints,  particularly  if  the  grade  is  at 
all  steep,  since  if  laid  down  grade  a  pipe,  after  being  placed 
in  position  and  before  the  next  is  laid,  tends  to  slide  away 
from  the  one  next  above  it  and  cause  a  break  in  the  inner 
surface  of  the  sewer  and  a  leaky  joint.  It  is  also  much  easier 
to  lay  pipe  with  the  bell  pointing  ahead,  and  the  cement  joint 
is  apt  to  be  firmer.  The  only  reason  advanced  for  laying  pipe 
down  hill  is  that,  the  lower  end  of  the  trench  being  ahead  of 
the  pipe,  any  ground-water  will  be  kept  drained  away  from 
the  sewer  construction.  This  is  discussed  in  Art.  73. 

For  lowering  into  the  trench  pipe  which  does  not  weigh 
more  than  100  pounds  a  convenient  method  is  to  use  a  rope 
of  f  to  i£  inch  diameter  with  a  hook  at  one  end.  The  hook 
is  passed  through  the  pipe  from  spigot  to  bell  and  then  back 
over  the  outside  to  the  middle  of  the  pipe  and  caught  on  the 
rope  there,  so  that  the  pipe  when  suspended  will  be  horizon- 
tal. Or  the  hook  may  pass  through  the  pipe  from  bell  to 
spigot  and  be  simply  caught  over  the  end  of  the  latter.  The 
pipe  is  lowered  over  the  edge  of  the  trench  by  one  man  and 
received  at  the  bottom  by  another  if  light,  or  by  two  if 
heavy,  the  hook  being  unfastened  and  pulled  up.  If  the  pipe 
weighs  more  than  100  pounds  two  men  will  be  required  to 


288 


SE  WERA  GE. 


lower  it,  which  they  do  by  each  holding  one  end  of  a  rope 
which  passes  through  it.  For  pipe  heavier  than  200  pounds 
it  is  advisable  to  use  an  ordinary  three-leg  derrick  with  light 
tackle-block.  The  pipe  is  then  suspended  by  a  rope  or  chain, 
with  a  hook  at  one  end  and  a  ring  at  the  other,  passed  through 
the  pipe  and  so  hooked  that  it  may  be  lowered  in  a  horizon- 
tal position.  A  convenient  arrangement  for  holding  the  pipe 
consists  of  a  hook  (Fig.  19),  which  should 
be  at  least  two  thirds  the  length  of  the 
pipe  and  very  strong  at  the  bend.  The 
ring  must  come  beyond  the  centre  of 
gravity  of  the  pipe  to  prevent  its  falling  off 
the  hook.  By  use  of  this  a  pipe  can 
while  suspended  be  entered  into  the  bell 


FIG.  19.— PIPE-LAYING  of  the  one  previously  laid  and  much  heavy 

HOOK.  lifting  by  hand  avoided. 

Another  method  of  entering  heavy  pipe  after  it  is  in  the 
trench  is  sufficiently  explained  by  the  illustration   Fig.   20. 


/////  //7777\. 


FIG.  20. — APPLIANCE  FOR  "ENTERING"  HEAVY  PIPE. 
This  is  made  of  wood  or  iron,  with  a  loose  wheel  on  either 
side  of  the  bar  at  the  bottom. 

Before  a  pipe  is  lowered  into  the  trench  a  "  bell-hole*' 
should  be  dug  where  its  bell  will  come,  of  such  size  that  when 
the  pipe  is  in  position  the  jointer  can  pass  his  hand  entirely 
under  and  around  the  front  of  the  bell.  It  is  convenient  to 


PRACTICAL   SEWER    CONSTRUCTION.  289 

have  a  stick  exactly  as  long  as  two  or  three  lengths  of  pipe, 
by  which  the  location  of  each  bell-hole  is  measured  from  pip^ 
already  laid,  the  bell-holes  being  dug  for  a  few  lengths  in 
advance  of  the  sewer. 

Two  men  should  be  employed  in  laying  sewer-pipe,  one 
straddling  the  pipe  last  laid,  the  other  in  the  trench  .just 
ahead  of  it.  The  latter  as  the  pipe  is  lowered  guides  it  into 
place  and  releases  the  hook  on  the  lowering-rope,  if  one  is 
used.  The  former,  holding  one  end  of  a  length  of  packing  in 
each  hand,  places  the  loop  thus  formed  under  and  around  the 
pipe  about  an  inch  from  the  spigot  end  and  guides  this  into 
the  bell  of  the  pipe  last  laid,  taking  care  that  the  packing  also 
enters  the  bell.  With  a  yarning-iron  he  then  pushes  the 
packing  up  against  the  shoulder  of  the  bell  all  around,  being 
first  sure  that  the  pipe  is  <4  home  "  in  the  bell.  The  other 
pipe-layer  meantime  supports  the  pipe  at  the  bell  end  and 
shoves  it  home.  The  grade-rod  and  plumb-bob  are  then 
used.  If  the  bell  end  is  too  high  (the  spigot  end  should  be 
all  right,  since  the  previous  pipe  is)  it  may,  if  the  soil  is 
loam  or  loose  clay  or  sand,  be  forced  down  a  quarter. of  an 
inch,  more  or  less,  by  standing  and  jumping  upon  the  top  of 
the  pipe.  (The  pipe-layer  should  never  rest  his  foot  inside 
the  pipe  to  force  it  down,  as  this  is  likely  to  break  the  bell  or 
even  the  pipe.)  If  the  soil  is  stiff  clay  or  gravel  the  pipe 
should  be  removed  and  the  trench  bottom  lowered  sufficiently 
with  the  shovel.  If  the  pipe  is  too  low  it  should  not  be  raised 
by  placing  a  stone  or  piece  of  wood  under  it,  but  should  be 
removed  and  fine  earth  placed  and  rammed  in  the  bottom  of 
the  trench.  By  means  of  the  plumb-bob  the  pipe  should  be 
centred  exactly  under  the  grade-line.  A  convenient  way  of 
doing  this  is  to  suspend  the  bob  from  the  cord  at  a  grade- 
plank,  being  careful  not  to  lower  the  cord  by  its  weight; 
then,  when  the  eye  is  so  placed  that  the  cord  and  plumb-bob 
string  coincide,  the  former  is  projected  by  the  eye  vertically 


2  pO  SEWERAGE. 

into  the  trench  and  should  cut  the  centre  of  the  pipe.  With 
a  circular  salt-glazed  pipe  the  centre  is  known  by  a  streak  of 
light  reflected  from  the  sky,  and  this  streak  should  be  bisected 
by  the  vertical  projection  of  the  grade-cord.  Another  plan 
for  obtaining  a  vertical  projection  of  the  grade-cord  is  to 
stretch  another  cord  a  foot  or  two  vertically  below  it.  But 
this  method  is  less  accurate  in  practice  than  the  other  and  is 
not  recommended.  The  grade-cord  cannot  be  stretched  so 
tight  that  it  will  not  sag  y1^  to  J  of  an  inch  at  the  centre,  but 
allowance  may  be  made  for  this  in  using  the  grade-rod.  The 
foreman  or  inspector  who  uses  the  grade-rod  will  need  to  have 
a  short  movable  plank  spanning  the  trench  just  ahead  of  the 
pipe  being  laid,  on  which  to  stand. 

As  soon  as  a  pipe  is  in  position  sufficient  earth  should  be 
placed  and  rammed  on  each  side  of  it  just  back  of  the  bell  to 
prevent  its  moving.  The  next  pipe  is  then  lowered  and  set, 
and  so  on. 

At  least  two  joints  behind  the  pipe  which  is  being  set  is 
another  man,  who  cements  the  joints.  The  cement  he  usually 
keeps  in  an  iron  pail  of  ordinary  size  (although  one  having 
the  shape  of  a  pan  would  be  better),  just  enough  being  mixed 
at  a  time  to  permit  his  using  it  all  before  it  stiffens.  If  there 
is  any  delay  in  laying  the  pipe  the  pail  should  be  cleaned  out 
lest  the  cement  set  in  it.  The  jointer  should  wear  rubber 
mittens,  and  a  small  trowel  will  be  found  more  convenient 
than  the  fingers  for  getting  the  cement  out  of  the  pail.  The 
cement  mortar  should  ordinarily  be  about  as  stiff  as  putty, 
but  if  the  trench  is  wet  it  should  be  as  dry  as  it  can  be  and 
have  any  cohesion.  The  jointer  takes  a  handful  of  mortar  in 
each  hand  and  presses  it  into  the  bell  all  around,  drawing  his 
hands  meantime  around  the  joint.  With  a  wooden  or  iron 
calking-tool  he  compacts  the  cement  in  the  joint,  adding 
more  as  is  necessary,  and  with  additional  mortar  he  makes  a 
neat  bevel  outside  the  bell,  continually  pressing  the  mortar 


PRACTICAL   SEWER    CONSTRUCTION.  291 

firmly  towards  the  bell.  This  bevel  should  not  be  flatter  than 
45°,  since  if  too  much  mortar  be  outside  the  bell  its  weight 
may  cause  it  to  fall  away  from  the  pipe  and  perhaps  draw 
with  it  the  mortar  from  inside  the  bell.  The  compacting  of 
the  cement  is  frequently  omitted,  but  is  necessary  if  tight 
joints  are  to  be  obtained.  *£ 

Just  behind  the  jointer  should  be  another  man,  who,  as 
soon  as  a  joint  is  made,  fills  the  bell-hole  carefully  with  fine 
earth  well  tamped,  and  then  fills  and  tamps  the  same  material 
under  and  around  the  rest  of  the  pipe  up  to  at  least  its 
middle.  His  tamping-bar  should  be  of  wood,  there  being 
danger  of  breaking  the  pipe  if  the  ordinary  iron  ones  are  used, 
and  with  a  face  about  2X4  inches.  If  the  trench  is  wet  so 
that  water  collects  in  the  bell-holes  the  mortar  is  likely  to 
become  softened  and  fall  out  of  the  joint.  To  prevent  this  a 
piece  of  cheese-cloth  may  be  wrapped  tightly  arjund  the  joint 
after  it  is  made,  as  specified  for  sub-drains;  or  the  bell-hole 
may  be  immediately  filled  with  concrete  thoroughly  com- 
pacted. The  latter  is  the  better  but  more  expensive  plan. 
Where  there  is  much  water  in  the  trench  it  is  strongly  recom- 
mended that  concrete  be  placed  not  only  in  the  bell-holes  but 
entirely  around  the  pipe  at  the  joints  (see  Art.  41). 

In  making  the  joint  it  is  quite  probable  that  some  cement 
will  be  squeezed  into  the  pipe,  forming  a  ridge  or  lumps  on 
the  inside.  To  remove  these  a  bag  or  disk  should  be  drawn 
through  the  pipe  past  the  joint  as  soon  as  it  is  finished,  which 
is  done  by  the  pipe-layers.  The  bag  may  be  an  ordinary 
cement  or  similar  sack,  somewhat  larger  than 
the  sewer,  filled  with  straw  or  excelsior  and  a 
rope  tied  around  its  mouth  and  carried  through 
the  sewer,  being  passed  through  each  pipe  as 


it   is  laid.      The  bag  should  fit  snugly  against     FlG-  21.— PIPE- 

„.-..,  T  CLEANING    DISK. 

the   pipe   all  around.       Instead  of  the  bag  a 

disk  of  heavy  rubber  packing  bolted   between   two    smaller 


2Q  2  SEWERAGE. 

wooden  disks  and  fastened  to  an  iron  rod  may  be  used,  being 
drawn  forward  as  in  the  case  of  the  bag.  The  rubber  disk 
should  be  slightly  larger  than  the  sewer. 

When  a  manhole  or  other  break  in  the  sewer  is  reached  in 
the  pipe-laying  the  last  pipe  before  reaching  and  the  first 
after  leaving  it  should  be  omitted  or  left  with  uncemented 
joint,  to  be  laid  while  the  manhole  or  other  appurtenance  is 
being  built.  This  is  on  account  of  the  probability  of  such 
pipe  being  disturbed  or  broken  during  the  construction  of  the 
masonry  before  it  has  been  walled  in.  In  this  or  any  case 
where  a  stretch  of  pipe  ends,  or  when  the  laying  is  temporarily 
stopped,  a  plug  should  be  inserted  in  the  end  of  the  last  pipe, 
and  a  bar  or  stake  driven  against  it  into  the  ground  or  nailed 
to  the  sheathing  to  hold  it  in  position.  The  last  joint  should 
be  left  uncemented  until  laying  is  renewed. 

In  setting  branch  specials  the  earth  where  the  special  will 
•come  should  be  so  excavated  as  to  permit  the  branch  to  rest 
upon  it  firmly  when  in  the  desired  position.  If  necessary 
earth  should  be  placed  and  tamped  under  the  branch  for  this 
purpose.  The  inspector  must  not  forget  to  examine  each 
branch  to  see  that  a  cover  is  cemented  in  it,  unless  the  house- 
connection  is  to  be  built  at  once,  and  also  to  mark  its  location. 
In  wet  soil  particularly,  uncovered  branches  may  give  rise  to 
serious  difficulty,  and  an  unlocated  branch  is  worse  than  none 
at  all. 

If  work  must  be  done  in  the  winter-time  great  care  should 
be  taken  to  prevent  the  mortar  from  freezing  and  to  keep  ice 
and  frozen  dirt  out  of  the  joints.  In  pipe-joints  this  is  not 
very  difficult  if  the  trenches  are  at  all  deep,  since  in  these  the 
temperature  seldom  falls  below  40°.  But  the  sand  for  mortar 
should  be  heated,  and  the  pipe  also,  to  insure  the  removal  of 
all  frost  from  the  bells  and  spigots.  In  shallow  trenches  the 
joints  should  be  covered  as  soon  as  possible  with  at  least  two 
feet  of  unfrozen  earth.  Care  should  be  taken,  particularly 


PRACTICAL   SEWER    CONSTRUCTION.  293 

•when  back-filling  is  dumped  from  excavator-buckets,  that  no 
frozen  lumps  fall  upon  the  sewer. 

The  back-filling  of  trenches  has  been  sufficiently  discussed 
in  Art.  54.  When  this  is  thrown  in  without  ramming  particu- 
lar care  should  be  taken  that  all  pipe  be  first  well  covered  with 
earth,  since  stones  and  frozen  lumps  invariably  roll  to  the  foot 
of  the  face-slope  of  the  back-filling  and  might  crack  unpro- 
tected pipe. 

It  is  frequently  necessary  to  cut  a  sewer-pipe  to  a  certain 
length  or  to  split  one  in  two  to  obtain  a  channel  for  a  man- 
hole bottom.  This  can  be  done  with  a  cold-chisel  and 
hammer,  a  light  cut  being  made  first  entirely  around  or  along 
the  pipe  and  this  gradually  deepened  until  the  pipe  of  itself 
breaks  in  two.  The  pipe  is  sometimes  filled  with  sand  well 
packed  before  the  cutting  is  begun,  but  this  is  not  necessary 
if  care  be  used. 

ART.  69.     BUILDING  MASONRY  SEWERS. 

Circular  or  egg-shaped  masonry  sewers  may  consist  of  a 
ring  of  masonry  of  uniform  thickness  throughout,  or  this  ring 
may  be  much  thicker  in  the  arch  than  in  the  invert,  or  there 
rrray  be  invert-backing  masonry  resting  upon  a  platform  foun- 
dation or  filling  the  irregular  spaces  of  a  rock  cut.  If  the 
sewer  comes  under  either  of  the  first  two  cases  it  is  usually 
made  entirely  of  either  brick  or  concrete,  owing  to  the 
expense  of  dressing  stone  to  make  tight  work  in  compara- 
tively thin  rings  and  to  give  a  smooth  interior  surface.  For 
massive  masonry,  as  in  invert-backing  or  heavy  arches,  stone 
can  be  used  and  is  in  many  cases  cheaper  than  brick.  In  many 
instances  concrete  may  be  cheaper  and  better  than  either. 

A  simple  ring  invert  can  be  used  only  where  the  soil  is 
firm  and  compact  enough  to  stand  when  given  the  shape  of 
the  outside  of  the  invert;  such  as  clay,  pure  or  mixed  with 
sand  or  loam.  If  it  will  not  retain  this  shape  while  the  sewer 


294 


SEWERAGE. 


is  being  built,  but  is  solid  enough  to  offer  good  foundation, 
as  damp  sand,  the  bottom  of  the  trench  may  be  given  a  flatter 
curve  and  lined  with  a  board  or  plank  cradle,  upon  which 
concrete  or  stone  masonry  is  placed  for  the  invert-backing,  to- 
be  lined  with  4  inches  of  brick-work.  In  rock  cuts  the  same 
plan  may  be  adopted,  since  it  is  usually  impracticable  to  bring 
the  rock  to  the  exact  shape  of  the  sewer  (see  Plate  VI,  Fig. 

10). 

If  artificial  foundation  is  necessary  this  usually  consists  of 
a  platform,  upon  which  the  masonry  rests,  and  which  is  placed 
directly  upon  the  trench  bottom  or  supported  upon  piles. 

If  the  arch  is  of  such  dimensions  that  the  thrust  is  more 
than  the  banks  can  be  trusted  to  sustain,  and  a  shape  similar 
to  that  shown  in  Plate  VI,  Fig.  5  or  9,  is  adopted,  concrete 
or  stone  masonry  may  be  used  for  the  side  walls,  and  a  plat- 
form is  generally  necessary  for  foundation  except  in  a  rock 
trench. 

Where  no  invert-backing  is  necessary  the  method  usually 
employed  is  as  follows:  Templets,  two  for  each  gang  of 
masons,  are  provided  conforming  to  both  the  inside  and 
outside  shape  of  the  sewer.  A  convenient  form  is  shown  in 
Fig.  22,  which  is  for  two  rings  of  brick.  This  is  made  of 


FIG.  22. — TEMPLET  FOR  BRICK  SEWERS. 

boards  or  plank,  2-inch  plank  being  sufficiently  heavy  for  any 
but  very  large  sewers.  A  templet  for  an  egg-shaped  sewer 
can  of  course  be  made  in  the  same  way.  Each  ring  of  brick 


PRACTICAL    SEWER    CONSTRUCTION.  295 

is  represented  in  the  templet  by  a  layer  of  plank,  its  inside 
edge  conforming  to  the  inner  surface  of  said  ring.  A  number 
of  fou; penny  or  fivepenny  nails  are  driven  along  the  edge  of 
each  plank  at  equal  intervals,  the  space  between  them  being 
the  thickness  of  a  brick  plus  that  of  the  mortar-joint,  usually 
about  2^  inches.  Each  templet  should  be  an  exact  duplicate 
of  the  other,  including  the  position  of  the  nails.  At  the  exact 
centre  A  of  the  cross-piece  a  notch  is  cut  or  a  nail  driven. 

When  the  bottom  of  the  trench  is  about  to  grade  one  of 
these  templets  is  set  in  a  vertical  position  so  that  the  centre 
of  the  cross-piece  is  exactly  in  the  centre  line  of  the  sewer, 
the  cross-piece  level,  and  the  inside  of  the  templet  at  the 
proper  grade  for  the  sewer-invert.  About  12  to  20  feet  along 
the  trench  the  other  templet  is  similarly  set,  the  sides  of  the 
templets  containing  the  nails  facing  each  other.  If  now  a 
cord  is  stretched  from  any  nail  in  one  templet  to  a  correspond- 
ing nail  in  the  other  the  excavation  should  be  exactly  the 
same  distance  outside  this  as  is  the  outside  of  the  templet. 
If  the  excavation  should  be  carried  too  far  it  must  be  rilled 
with  sand  well  rammed,  or  with  good  cement  mortar. 

The  cord  is  now  stretched  between  the  lowest  nails  in  the 
outer  rings  of  the  two  templets,  and  the  brick  laid  to  this  line 
from  end  to  end.  The  cord  is  now  shifted  to  the  next  nail 
in  the  same  ring  and  the  next  row  of  brick  laid.  When  two 
or  three  courses  have  been  laid  on  one  side  of  the  centre  the 
same  number  are  laid  on  the  other  side,  and  both  sides  of  the 
sewer  are  carried  up  simultaneously,  for  which  reason  the 
masons  usually  work  in  gangs  of  2,  4,  6,  or  8.  Not  more 
than  the  last  number  can  work  to  advantage  on  one  section  of 
invert,  but  several  sections  may  be  under  construction  simul- 
taneously. 

When  four  or  five  courses  have  been  laid  a  plank  is  placed 
on  these  for  the  masons  to  stand  on,  and  the  brick-work  is 
continued  row  by  row,  each  row  being  laid  carefully  to  line. 


296  SEWERAGE. 

The  bricks  of  succeeding  courses  should  break  joints  at  least 
3  inches. 

After  the  outer  ring  has  been  completed  to  the  springing- 
line  the  next  is  laid  in  the  same  way.  The  bricks  of  each 
ring  should  be  bedded  in  mortar  at  least  -J  inch  thick,  and 
every  joint  should  be  completely  filled.  Considerable  diffi- 
culty will  be  found  in  getting  any  but  experienced  sewer- 
masons  to  lay  the  brick  radially,  but  smooth  work  cannot  be 
obtained  otherwise  and  this  must  be  insisted  upon.  All 
joints  should  be  carefully  struck.  If  they  are  not  they  should 
be  afterward  raked  out  and  pointed. 

If  the  brick  do  not  absorb  more  than  2  or  3  per  cent  of 
water  in  the  absorption  test  they  should  not  be  wet,  as  they 
could  not  then  be  made  to  stay  in  place.  But  if  they  take  more 
water  than  this  they  should  be  wet  just  before  using.  A 
quick  test  for  this  on  the  ground  is  to  drop  a  brick  into 
mortar  and  remove  it.  If  the  mortar  does  not  in  two  or 
three  minutes  grow  dry  where  it  touches  the  brick  they  prob- 
ably do  not  need  wetting. 

The  mortar  is  usually  mixed  in  a  box  on  the  bank  (it 
should  never  be  mixed  on  the  ground  for  any  purpose)  and 
lowered  into  the  trench  in  a  pail  by  a  rope  provided  with  a 
hook,  where  it  is  emptied  onto  the  mortar-boards.  These 
boards  are  usually  24  to  30  inches  square.  The  brick  is 
placed  in  hods  on  ihe  bank  and  lowered  to  the 
masons.  A  convenient  form  of  hod  is  shown 
by  Fig.  23,  which  is  made  of  sheet  iron  and 
can  be  quickly  filled  and  emptied.  The  ma- 
terial is  usually  lowered  by  hand  for  small 
sewers,  and  the  man  who  does  this  should 
have  a  heavy  leather  palm-piece  for  each  hand. 
FIG.  23.— HOD  FOR  A  leather  glove  or  mitten  would  not  last  a 
LOWERING  BRICK.  day  of  hard  usage  at  such  work.  To  permit 
of  lowering  the  material  a  platform  is  usually  thrown  across 


PRACTICAL   SEWER    CONSTRUCTION.  297 

tlu-  trench  above  where  the  masons  are  working.  If  stone  is 
being  laid,  or  much  material  is  to  be  used  at  one  place,  or  the 
trench  is  quite  deep,  the  material  may  be  lowered  by  a  wind- 
lass set  in  a  portable  frame  or  by  a  derrick.  If  excavating- 
machinery  is  being  used  this  may  be  utilized  for  lowering  the 
material. 

As  the  invert  of  the  sewer  rises  it  becomes  difficult  for  the 
masons  to  lay  the  brick,  and  the  material  if  in  the  bottom  of 
the  sewer  is  too  far  from  the  work.  A  platform  is  then 
necessary  and  can  be  made  by  sawing  plank  of  such  length  as 
to  be  at  the  desired  elevation  when  placed  horizontally  cross- 
wise of  the  sewer.  Three  or  four  of  these  can  be  thus  laid, 
with  a  few  brick  under  the  centre  of  each  as  additional  support, 


FIG.  24. — MASONS'  PLATFORM  FOR  BRICK  SEWERS. 

and  a  platform  of  loose  plank  placed  over  them.  But  this  is 
apt  to  distort  the  green  brick-work  at  the  ends  of  the  cross- 
plank,  and  it  is  better  to  have  a  number  of  plank  cut  to  the 
shape  of  the  sewer-invert  cross-section,  which  will  distribute 
the  load  along  their  entire  length,  and  to  rest  the  platform 
on  these  (see  Fig.  24). 

When  one  section  of  invert  is  completed  one  of  the 
templets  is  moved  ahead  the  length  of  a  section  and  set.  The 
other  will  not  be  needed  by  the  masons,  since  one  end  of  the 
cord  will  be  fastened  to  nails  stuck  into  the  joints  of  the 
invert  just  completed.  The  second  templet  can,  however,  be 
used  to  advantage  for  grading  the  trench  ahead  of  the  masons. 

In  bonding  the  new  work  with  that  previously  laid  (the 


298  SEWERAGE: 

end  of  which  should  invariably  be  racked  back)  all  loose 
brick  and  mortar  should  be  removed,  and  the  brick  cleaned 
and  wetted  before  applying  fresh  mortar. 

The  arch  of  the  sewer  is  built  upon  a  "  centre,"  which  is 
removed  when   the  arch  is  completed   and   the   mortar  suffi- 


FIG.  25. — CENTRE  FOR  BRICK  SEWERS. 

ciently  set.  The  centre  usually  consists  of  lagging  supported 
by  curved  ribs  of  wood  or  iron.  Probably  the  most  common 
form  is  that  shown  in  Fig.  25.  To  templets  similar  in  form 
and  general  construction  to  those  for  the  invert  are  nailed 
lagging-strips  about  I  inch  thick  and  ij  inches  wide,  spaced 
2\  inches  between  centres,  there  being  a  templet  at  each  end 
and  intermediate  ones  spaced  3  or  4  feet  apart.  The  lagging- 
pieces  should  be  perfectly  parallel,  as  their  edges  are  used  for 
lining  the  brick-work.  If  the  radius  of  the  arch  exceeds  2 
or  3  feet  the  lagging  may  be  of  ij-  or  2-inch  by  3^-inch 
strips,  spaced  4^  inches  between  centres;  but  the  2j-inch 
spacing  will  give  a  better  surface  whatever  the  radius.  The 
templets  should  lack  3  or  4  inches  of  being  complete  semi- 
circles, so  that  when  in  position  the  bottom  of  the  centre  may 
be  about  i£  or  2  inches  above  the  springing-line  of  the  arch. 
The  centre  may  be  held  in  position  by  a  triangular  frame 
under  each  templet,  supporting  a  plank  along  each  side  of  the 
sewer,  upon  which  the  centre  rests,  it  being  raised  to  exact 
position  by  wedges,  as  shown  in  Fig.  25.  When  the  arch  is 


PRACTICAL    SEWER    CONSTRUCTION.  299 

completed  the  wedges  are  knocked  out  and  the  centre  drops 
onto  the  two  planks  and  can  be  pulled  forward,  sliding  upon 
these.  It  is  sometimes  difficult,  particularly  with  large  and 
heavy  centres,  to  draw  them  out,  and  to  facilitate  this  a  light 
temporary  track  has  in  some  instances  been  built  under  the 
•centre,  which  was  placed  upon  wheels  which  rose  2  or  3 
inches  above  the  track  when  the  centre  was  wedged  up  into 
position.  By  knocking  out  the  wedges  the  centre  drops  onto 
the  track  and  can  be  readily  rolled  forward.  The  use  of  rings 
of  angle-iron  to  support  the  lagging  has  given  good  satisfaction. 
The  cost  of  setting  up  and  removing  the  center  is  an  appreciable, 
.sometimes  a  considerable,  item  of  cost,  and  effort  should  be  made 
to  reduce  this  to  a  minimum.  Several  designs  of  collapsible 
centers,  both  wood  and  steel,  have  been  designed  with  the  idea  of 
facilitating  removal. 

The  arch  should  be  built  up  at  a  uniform  rate  on  both 
sides  at  once,  and  the  last  row  of  brick  to  be  laid  in  each  ring 
should  be  at  the  crown  and  should  be  driven  tightly  into  place 
as  a  key.  It  may  be  necessary  to  split  brick  for  this  purpose, 
but  it  is  better  to  have  on  hand  a  number  of  thin  arch-brick 
(of  wedge-shaped  section),  hard  and  tough,  which  will  stand 
driving.  The  outside  of  the  arch  is  usually  plastered  with  £ 
to  \  inch  of  mortar.  The  centre  should  be  left  under  until 
the  mortar  is  so  set  that  there  is  no  danger  of  the  arch 
becoming  deformed  if  it  is  drawn,  the  time  varying  with  the 
character  of  cement,  shape  and  thickness  of  the  arch,  and 
other  details  of  construction.  It  is  probably  well  in  most 
cases  to  back-fill  to  the  crown  of  the  arch  as  soon  as  it  is  com- 
pleted. But  if  the  soil  is  wet,  like  muck,  or  if,  when  excavat- 
ing-machinery  is  used,  the  buckets  usually  contain  consider- 
able water,  no  back-filling  should  be  done  until  the  mortar  is 
thoroughly  set. 

After  the  removal  of  the  centre  the  arch  masonry  will 
ordinarily  be  found  somewhat  uneven,  with  mortar  adhering 


300  SEWERAGE. 

in  flat  lumps  to  a  large  part  of  its  surface.  These  should  be 
removed  and  the  joints  so  pointed  as  to  render  the  surface 
more  even;  or  the  whole  inside  of  the  arch  may  be  plastered. 

If  there  is  masonry  backing  to  the  invert  this  is  usually 
laid  as  uncoursed  rubble  or  concrete  up  to  within  4j  inches 
of  the  invert-surface,  the  templet  having  been  set  to  indicate 
this,  and  the  brick  lining  is  then  laid  as  above  described.  If 
concrete  is  used  and  is  not  carried  to  the  sides  of  the  trench 
(see  Plate  VI,  Fig.  9)  a  form  of  plank  is  used,  inside  which 
the  concrete  is  rammed,  and  the  plank  removed  when  this  is 
set.  If  the  trench  is  sheathed  and  the  concrete  is  built 
against  the  sheathing  this  cannot  be  pulled,  but  must  be  left 
in  or  cut  off  above  the  concrete.  If  stone  masonry  is  used 
for  invert-backing  it  is  better  to  lay  the  course  of  stone  next 
to  the  brick  lining  with  radial  beds. 

If  concrete  is  used  for  the  entire  sewer  special  forms  must 
be  made  for  each  size  of  sewer,  several  sets  being  in  use 
by  each  gang.  The  form  for  the  invert  may  be  made  similar 
to  an  arch-centre,  except  that  the  lagging  must  make  tight 
joints  (its  edges  being  bevelled  to  permit  of  this)  and  only  the 
two  or  three  on  the  bottom  be  fastened  to  the  templets. 
This  form  is  fixed  in  position,  concrete  is  placed  in  the 
bottom,  between  the  lagging  and  the  earth,  and  rammed;  one 
or  two  strips  of  lagging  are  then  slipped  into  position  on  each 
side  and  concrete  placed  and  rammed  behind  these;  more 
strips  are  added  and  concrete  rammed  behind  them,  and  so 
on  until  the  concrete  is  brought  to  the  springing-line  of  the 
arch.  The  forms  should  not  be  removed  until  the  concrete 
is  set.  There  is  much  danger  that  in  this  invert  construction 
dirt  and  stones  will  get  into  the  concrete,  to  its  detriment, 
and  great  care  must  be  taken  to  avoid  this.  The  forms  must 
be  strongly  braced  down  from  the  bank,  to  resist  their  ten- 
dency to  rise  when  the  concrete  is  rammed.  The  concrete 
should  be  just  wet  enough  to  permit  water  to  be  brought  to 


PRACTICAL    SEWER    CONSTRUCTION.  301 

the  surface   by  light  ramming.     No  heavy  rammers  should  be 

used. 

The  concrete  should  contain  no  stone  larger  in  any  dimension 
than  one-third  the  thickness  of  the  sewer  shell.  Gravel  is  found 
to  make  more  water-tight  concrete  than  broken  stone,  but  to 
make  it  less  strong.  More  important  for  water-tightness  is  the 
careful  grading  of  materials,  the  sizes  changing  gradually  from 
sand  up  to  the  coarsest  stone  so  as  to  obtain  the  maximum  density. 
While  placing  the  concrete,  spades  or  other  instruments  with 
flat  blades  should  be  continually  pushed  down  between  the  inside 
form  and  the  cement  just  placed,  and  moved  slightly  back  and 
forth  so  as  to  press  the  larger  stones  away  from  the  form,  leaving 
the  finer  material  there  and  thus  securing  a  smoother  surface 
without  pockets  or  air  holes. 

In  the  placing  of  the  concrete  there  is  great  possibility  for 
effecting  economy.  Perhaps  the  most  economical  plant  for  this 
was  one  employed  in  Baltimore,  where  a  Hains  mixer  was  placed 
on  a  trestle  straddling  the  trench,  this  trestle  being  moved  ahead  as 
the  sewer  was  constructed  so  that  the  concrete  always  fell  directly 
from  the  mixer  onto  the  point  where  it  was  desired  in  construction ; 
the  only  handling  required  being  spreading  the  material  by 
hoes  or  shovels  and  the  use  of  the  spade  as  described  above. 
In  other  instances  the  mixer  is  placed  upon  a  car,  cart  or  movable 
platform  and  the  concrete  is  run  in  metal  or  wooden  troughs 
directly  from  the  discharge  spout  of  the  mixer  onto  the  work. 
By  using  a  long  trough  in  two  or  three  sections,  which  sections 
are  moved  every  few  minutes,  practically  no  spreading  of  the 
concrete  is  required,  but  it  can  be  discharged  exactly  where 
wanted.  In  other  instances  it  may  be  cheaper  to  keep  the  con- 
crete mixer  at  one  point  for  a  considerable  stretch  of  sewer  and 
convey  the  concrete  to  the  work  either  by  wheelbarrows  or  by 
a  trench  machine  or  cableway  such  as  is  used  in  excavating  the 
trench. 

For  making  a  concrete  arch,  a  centre  is  used  with  close  lagging, 


302 


SEWERAGE. 


or  an  open-lagged  centre  may  be  covered  with  sheet  metal,  as 
on  the  Wachusett  Aqueduct  mentioned  above.  The  outside  form 
may  be  constructed  as  shown  in  Fig.  26,  the  forms  being  placed 
3  to  5  feet  apart,  the  lagging  being  loose  and  put  in  one  strip 
at  a  time. 


FIG.  26. — FORM  FOR  CONCRETE  ARCH. 

In  some  cases  the  forms  for  both  invert  and  arch  are  com- 
bined in  one  cylindrical  form.  The  invert  for  a  width  of  a  foot 
or  two  is  first  completed  to  the  correct  grade,  and  while  this  is 
still  fresh  the  cylindrical  form  is  rested  upon  it  and  braced  in 
exact  line,  an  outside  form  for  the  invert  is  placed  if  this  is  necessary, 
and  concrete  is  deposited  between  the  forms  on  both  sides,  the 
two  sides  being  carried  up  uniformly.  Unless  the  cylindrical 
form  is  well  braced  both  horizontally  and  vertically  it  will  be 
lifted  by  the  concrete,  and  careful  attention  must  be  paid  to  this. 
As  soon  as  the  concrete  has  reached  the  springing  line  the  form 
for  the  outside  of  the  arch  is  placed  in  position,  a  board  at  a  time, 
as  described  above,  and  that  section  of  sewer  completed.  This 
makes  the  entire  sewer  a  monolith,  which  has  many  advantages. 

There  have  recently  come  into  quite  general  use  forms  of  sheet 
steel  provided  with  interior  braces  to  hold  it  to  shape;  such  forms 
being  generally  semi-cylindrical,  with  the  braces  so  arranged  that 
the  form  can  be  partially  or  wholly  collapsed  to  make  easier  the 


PRACTICAL    SEWER    CONSTRUCTION.  303 

removal  of  the  form  from  the  completed  sewer.  In  some  instances 
the  forms  are  complete  cylinders,  arranged  so  that  they  can  be 
collapsed  for  drawing.  These  are  usually  to  be  preferred  to 
wooden  lagging,  as  they  are  absolutely  water-tight,  thus  preventing 
the  escape  of  water  from  the  concrete,  which  water  would  carry 
with  it  a  considerable  part  of  the  cement;  they  also  giving  a 
smoother  surface.  They  are  generally  more  durable  and  easier 
to  handle  than  wooden  forms.  In  constructing  the  Wachusett 
Aqueduct,  n  feet  6  inches  in  diameter,  a  wooden  center  was 
covered  with  galvanized  iron,  greased  with  black  oil,  this  probably 
being  the  forerunner  of  the  present  all-metal  centers. 

When  reinforcement  is  used  the  placing  of  the  concrete  is 
somewhat  interfered  with  by  the  rods  or  other  metal,  but  care  must 
t>e  taken  to  keep  these  in  the  position  which  they  are  designed  to 
occupy.  It  will  ordinarily  be  necessary  to  place  temporary  blocks 
on  the  form,  against  which  the  reinforcement  rests,  each  set  of 
blocks  (which  will  usually  be  in  the  form  of  a  strip),  being  removed 
as  the  concrete  reaches  it.  It  is  very  important  that  the  reinforce- 
ment be  entirely  covered  with  the  mortar  of  the  concrete,  and  for 
that  reason  it  is  desirable  to  use  narrow  spades  for  tamping  the 
concrete  around  the  reinforcement  rods.  Also  it  is  generally 
desirable  to  make  the  concrete  somewhat  thinner  when  reinforce- 
ment is  used  than  would  be  necessary  otherwise. 

In  a  number  of  instances  concrete  sewers  have  been  built  of 
voussoir  blocks  which  have  been  made  outside  the  trench,  usually 
at  a  yard  near  the  railroad  siding  where  the  material  is  delivered. 
Generally  from  four  to  six  or  eight  blocks  are  used  in  each  ring 
of  the  sewer.  One  patented  construction  leaves  grooves  in  the 
edges  of  the  blocks,  in  which  grooves  are  placed  reinforcing  rods, 
the  rest  of  the  groove  then  being  tilled  with  cement  mortar.  Clay 
voussoir  blocks  also  have  been  similarly  used. 

Concrete  sewers  have  been  built  in  a  "travelling  mould" 
(Ransome  method),  by  use  of  which  the  entire  sewer  is  con- 
structed continuously,  foot  by  foot.  A  core  in  the  shape  of  a 
ribbon  which  can  be  readily  withdrawn  after  use  (Chenoweth 


304  SEWERAGE. 

system)  has  been  used  for  small  concrete  sewers,  to  which  the 
use  of  the  ordinary  centre  and  form  is  not  adapted. 

ART.  70.     BUILDING  MANHOLES  AND  OTHER 
APPURTENANCES. 

These  can  most  conveniently  be,  and  usually  are,  built  of 
brick;  although  some  have  been  built  of  concrete,  a  collapsible 
form  for  the  inside  having  been  designed  in  at  least  one  case.  The 
foundation  is  sometimes  of  brick,  but  concrete  is  better  in  most 
cases.  A  stone  slab  set  on  concrete  makes  a  good  bottom  for 
catch-basins. 

The  channel  through  a  pipe-sewer  manhole  is  sometimes 
built  of  brick,  but  a  split  pipe  is  better.  If  brick  be  used,  the 
inside  of  the  channel  should  be  plastered  with  a  coat  of  neat 
Portland  cement.  If  any  branch  channel  in  a  manhole  is  not  to 
be  used  at  once  it  should  be  temporarily  closed  to  prevent  deposits 
forming  in  it.  The  bench  may  be  built  up  of  brick  plastered  on 
top  with  cement,  or  of  concrete.  Or  the  whole  manhole  bottom 
may  be  of  concrete,  a  wooden  or  sheet-metal  core  being  slipped 
into  the  opposite  pipes  and  spanning  the  manhole  to  give  the  shape 
to  the  channel. 

In  leaving  the  manhole  opening  in  a  brick  sewer  the  end 
brick  in  every  alternate  course  of  the  outside  ring  may  be  laid 
radially,  thus  presenting  toothing  protruding  at  right  angles  to 
the  sewer-barrel.  In  this,  steps  with  horizontal  treads  can  be  built 
of  brick  trimmed  to  the  necessary  shape,  from  which  the  manhole 
can  be  carried  up  without  danger  of  its  sliding  off  the  sewer. 

To  insure  having  the  manhole  of  the  proper  size  and  shape 
a  board  templet  may  be  used,  being  laid,  in  pipe-sewer  man- 
holes, upon  the  concrete  foundation  when  this  has  set,  and 
the  brick  started  by  it  and  carried  vertically  to  the  proper 
height.  Another  templet  24  inches  diameter  is  fastened  at 
the  level  of  the  top  of  the  brick-work,  its  centre  vertically 
above  that  of  the  bottom  templet.  Cords  are  strung  from 
the  edge  of  the  top  templet  to  the  top  of  the  vertical  part  of 


PRACTICAL    SEWER    CONSTRUCTION.  305 

the  brick  wall,  spaced  about  2  feet  apart  around  its  circum- 
ference, and  the  brick  laid  to  these.  An  experienced  man- 
hole mason,  however,  can  build  almost  as  symmetrical  a 
manhole  by  eye  only,  and  more  quickly  than  if  strings  are 
used. 

When  the  wall  is  about  2  or  3  feet  high  the  benches  and 
channels  of  the  bottom  may  be  constructed.  It  is  well  to  lay 
plank  in  the  bottom  over  the  channels  temporarily,  to  keep 
mortar  and  dirt  out  of  them  and  out  of  the  sewer  during  con- 
struction, as  well  as  to  hold  the  brick  and  mortar  being  used. 
The  first  step  should  be  placed  about  1 8  inches  or  2  feet  above 
the  bench.  When  the  wall  is  about  4  feet  high  four  piles  of 
brick,  each  8  inches  square  and  about  3  feet  high,  may  be 
set  on  the  bottom  of  the  manhole  and  a  platform  of  short 
loose  plank  be  placed  on  these,  entirely  filling  the  manhole. 
This  holds  the  mason,  brick,  and  mortar  until  another  3  feet 
are  built,  when  a  second  platform  is  similarly  placed  3  feet 
higher.  These  are  of  course  removed  when  the  brick-work  is 
completed. 

The  brick  in  a  manhole  may  be  laid  as  all  headers,  all 
stretchers,  all  on  end  with  their  edges  exposed,  or  a  combina- 
tion of  any  two  or  all  of  these.  Bats  may  be  used  in  large  or 
small  proportion  or  not  at  all.  A  strong  manhole  can  be 
built  by  using  three  courses  of  stretchers  to  one  of  headers, 
all  whole  brick,  until  a  diameter  of  about  3  feet  is  reached, 
and  from  there  to  the  top  using  three  courses  of  squared  bats 
to  one  of  headers.  The  outside  of  the  manhole  should  be 
plastered  as  the  wall  is  built,  since  it  may  be  impossible  to 
reach  it  afterward.  The  head  should  be  set  and  the  opening 
back-filled  as  soon  as  the  brick-work  is  completed. 

If  the  manhole  is  shallow,  or  for  any  other  reason  the 
diameter  is  to  be  rapidly  reduced  towards  the  top,  this  is 
ordinarily  done  by  making  each  ring  of  brick  a  little  smaller 
than  the  one  below,  the  diameter  of  the  manhole  being 
reduced  by  I  to  4  inches  with  each  ring.  Or  it  may  be 


306  SEWERAGE. 

arched  (Plate  IX,  Fig.  2),  when  the  back-filling  around  it 
should  be  thoroughly  tamped  to  assist  in  taking  the  thrust, 
In  the  case  of  flush-tanks  particularly,  a  flat  iron  ring  is  some- 
times built  in  the  outside  of  the  brick-work  at  the  bottom  of 
the  arch  as  a  precaution. 

Flush-tanks  are  built  in  a  manner  similar  to  the  above. 
These,  except  at  the  very  top,  and  catch-basins  and  inlets,  are 
usually  larger  in  diameter  than  manholes,  and  are  built 
throughout  of  whole  brick.  Extra  care  should  be  taken  to 
have  all  joints  filled  with  cement  and  tight,  and  the  work  well 
bonded.  After  the  cement  in  flush-tanks  and  catch-basins 
has  fully  set  they  should  be  given  on  the  inside  two  or  three 
washes  of  neat-cement  grout,  laid  on  with  a  whitewash  or 
similar  brush,  care  being  taken  to  cover  the  entire  sur- 
face with  each  coat,  which  should  be  allowed  to  dry  before  the 
next  is  applied.  This  will  seldom  fail  to  give  a  tight  wall. 

Concrete  would  seem  to  be  especially  adapted  to  flush-tanks,  as 
it  can  be  made  water-tight  more  readily  than  can  brick.  The 
concrete  should  be  made  of  a  rich  mixture,  with  an  aggregate  of 
sizes  grading  gradually  from  the  largest  to  the  sand.  Gravel  will 
generally  give  more  impervious  concrete  than  stone.  It  should 
be  mixed  just  wet  enough  to  flow  into  place  in  the  form  when 
joggled  with  a  shovel. 

No  water  should  be  turned  into  the  trench  for  flushing  or 
other  purposes  before  the  cement  in  these  appurtenances,  as 
well  as  in  the  sewer,  has  set. 

If  masonry  in  either  sewers  or  their  appurtenances  is  laid 
in  freezing  weather  special  measures  and  precautions  should 
be  taken.  The  sand,  stone,  brick,  and  water  should  all  be 
heated  before  being  used,  and  special  care  taken  to  see  that 
no  ice  or  frozen  dirt  is  in  the  mortar,  on  the  stone  or  brick, 
around  the  sub-drain,  under  the  pipe,  or  under  or  behind  the 
brick  or  concrete  sewer-invert.  To  insure  the  last  it  is  well 
to  take  out  the  last  foot  or  two  of  trench  just  before  the  sewer 
is  to  be  laid  in  it.  If  any  frozen  earth  is  found  under  the 


PRACTICAL    SEWER    CONSTRUCTION.  307 

sewer  grade  it  should  be  removed  and  replaced  by  sand  or 
gravel  thoroughly  rammed. 

The  water  for  mortar  can  be  conveniently  heated  by 
injecting  into  it  steam  (as  the  exhaust  from  a  pump-  or  exca- 
vator-engine), it  being  kept  in  several  hogsheads  or  oil- 
barrels.  The  brick  and  stone  can  be  heated  by  piling  them 
as  in  brick-kilns  and  burning  a  wood  fire  under  them;  and  the 
sand  by  being  piled  over  these,  or  in  large  iron  pans  such  as 
are  used  for  heating  asphalt,  or  over  five-  to  ten-foot  lengths  of 
large  sheet  iron  pipe  in  which  wood  fires  are  kept  burning. 

ART.  71.    FOUNDATIONS. 

Piles  are  ordinarily  used  for  sewer-foundations  in  soft  soil. 
They  usually  support  a  timber  platform,  but  in  some  instances 
concrete  is  placed  directly  upon  and  around  their  heads.  For 
driving  them  the  ordinary  pile-drivers  are  used,  or  they  are 
sunk  by  the  water-jet.  If  they  are  to  support  platform 
timbers  they  must  be  driven  carefully  to  line  and  sawed  off 
accurately  to  grade.  It  will  sometimes  be  advisable  to  drive 
the  piles  before  the  excavation  has  proceeded  very  far,  using 
piles  considerably  longer  than  actually  required,  as  the  jarring 
of  the  banks  of  the  trench  may  thus  be  avoided,  as  well  as  the 
inconvenience  of  moving  the  driver  through  or  over  a  trench 
full  of  braces.  The  objection  to  this  plan,  aside  from  the 
cost  of  the  additional  length  of  the  piles,  is  that  they  interfere 
with  the  excavation. 

In  moving  an  ordinary  pile-driver  through  the  trench  it 
will  be  necessary  to  remove  the  braces  ahead  of  it.  But  no 
brace  should  be  removed  until  another  has  been  inserted 
behind  the  driver-frame  between  the  same  rangers  and  as 
close  to  the  first  as  possible.  This  trouble  might  be  avoided 
in  many  cases  by  placing  the  pile-driver  on  a  track,  on  a  level 
with  the  ground,  over  the  centre  of  the  trench;  or  the  track 
may  be  on  the  surface  at  one  side  of  the  trench.  The  driver 


308  SEWERAGE. 

is  then  provided  with  movable  hammer-guides,  which  can  be 
lowered  into  the  trench  and  raised  with  ease.  The  use  of  the 
steam-hammer  pile-driver  is  often  advantageous,  and  in  sandy 
soils  the  water-jet  can  be  used  to  advantage.  Neither  of 
these  last  is  interfered  with  in  ks  operation  by  the  bracing. 

The  dimensions  and  construction  of  the  platform  follow 
the  rules  for  ordinary  foundations.  There  is  usually  but  one 
set  of  timbers  under  the  planking,  which  is  in  most  cases 
composed  of  one  or  two  layers  of  2-inch  to  4-inch  plank,  as 
in  Plate  VI,  Figs.  3,  5,  and  6;  although  in  some  instances 
heavy  timbers  are  used,  as  in  Plate  VII,  Fig.  10.  Any 
timber  which  is  to  be  placed  where  it  will  not  be  continually 
wet  should  be  creosoted. 

If  a  platform  is  used  without  piling,  sills,  longitudinal  or 
cross,  should  be  placed  under  the  planking,  although  in  the 
case  of  small  sewers  these  may  consist  of  lengths  of  2-inch 
plank  only.  Platforms  without  piling  or  heavy  sills  are  of 
little  permanent  service  under  large  sewers,  but  during  con- 
struction may  serve  to  prevent  local  distortion  of  the  masonry 
before  the  cement  has  set.  One  or  two  lines  of  plank  placed 
lengthwise  under  a  pipe  sewer,  however,  are  in  many  cases  of 
permanent  value,  back-filling  being  thoroughly  filled  and 
rammed  between  the  pipe  and  the  plank. 

Among  the  best  of  our  woods  for  foundations  are  the 
cedar,  oak,  elm,  alder,  and  beech.  All  bark  should  be 
removed  and  the  sap  dried  out  from,  piling  or  sawed  timber. 
The  platform  timbers  should  be  fastened  to  the  piles  with 
iron  drift-bolts  or  treenails. 

ART.  72.     PUMPING  AND  DRAINING. 

Next  to  quicksand,  water  is  probably  the  worst  enemy  of 
the  sewer-contractor  and  requires  a  large  share  of  £he  atten- 
tion of  the  engineer.  If  there  is  but  a  small  trickle  or  ooze 


PRACTICAL   SEWER    CONSTRUCTION.  309 

of  water  into  the  trench  it  may  interfere  but  little  with  the 
excavating,  and  will  collect  at  points  in  the  bottomed  trench 
whence  it  can  be  removed  at  intervals  by  a  bucket.  If  the 
amount  becomes  somewhat  greater  it  may  still  be  handled 
without  the  use  of  sub-drains,  that  from  where  the  pipe  has 
been  laid  being  shut  off  by  the  back-filling. 

The  amount  from  the  trench  ahead  of  the  sewer  may  need 
to  be  pumped,  however.  For  removing  small  quantities  of 
water  from  a  trench  probably  nothing  is  better  than  a 
diaphragm-pump.  Tin  "  boat-pumps  "  are  often  used,  but 
will  not  handle  so  much  water,  are  less  economical  of  power, 
and  are  not  so  convenient  as  the  diaphragm-pump;  they  can, 
however,  be  used  in  trenches  more  than  20  feet  deep,  where 
the  diaphragm  is  hardly  practicable.  Under  favorable  condi- 
tions a  diaphragm-pump  can  be  made  to  raise  5000  or  6000 
gallons  per  hour.  Diaphragm-pumps  can  be  used  in"  deep 
trenches  by  placing  a  second  pump  upon  a  platform  half  way 
down  the  trench,  which  discharges  the  water  into  a  tub,  from 
which  the  first  pump  raises  it  to  the  surface.  Or  the  upper 
pump  may  not  be  used,  but  a  trough  may  carry  the  discharge 
from  the  lower  one  to  an  opening  left  temporarily  in  the  sewer 
at  a  point  where  the  cement  is  so  set  as  to  be  uninjured  thereby, 
the  water  flowing  through  the  sewer  to  its  outlet. 

A  sump-hole  of  ample  size  should  be  made  in  the  bottom 
of  the  trench  to  receive  the  suction-pipe,  which  should  be 
provided  with  a  strainer  at  the  bottom.  If  the  material  is 
sand  or  soft  ground  it  is  well  to  place  a  pail  or  keg  in  the 
sump  to  keep  the  end  of  the  suction-pipe  from  being  buried, 
the  top  of  the  pail  being  just  below  the  level  of  the  trench 
bottom.  The  pail  should  be  watched  and  mud  kept  from 
running  over  its  edge.  The  excavation  should  usually  be  so 
carried  on  that  the  whole  trench  slopes  toward  the  sump-hole, 
each  laborer  seeing  that  the  water  flows  through  his  section  to 
the  next  lower. 


310  SEWERAGE. 

Where  a  sub-drain  is  being  laid  the  water  is  frequently 
permitted  to  flow  from  the  trench  under  excavation  to  and 
through  this.  In  many  if  not  most  soils  this  is  bad  policy, 
since  it  leads  to  a  silting  up  of  the  drain  by  the  large  amount 
of  material  washed  in  from  the  trench.  It  is  better  in  most 
cases  to  leave  or  make  a  dam  at  the  upper  end  of  the  com- 
pleted trench,  and  place  a  sump-hole  just  ahead  of  this  and 
below  grade,  from  which  the  water  is  pumped.  When  a  sec- 
tion of  20  or  30  feet  has  been  excavated  to  grade  another 
dam  and  sump-hole  can  be  placed  at  the  head  of  this  section 
and  the  others  removed,  the  sump-hole  being  filled  with  sand 
or  gravel  or  other  good  material  well  rammed.  The  sub-drain 
will  then  be  in  good  working  condition  to  keep  the  trench  dry 
during  pipe  laying. 

Where  a  sub-drain  is  started  from  a  sump-hole,  or  that 
lower  down  the  line  is  found  to  be  too  small  to  carry  the 
water  coming  to  it,  a  pump  must  be  placed  at  this  point  also 
to  remove  the  water  from  the  sub-drain  which  is  to  be  laid 
beyond  it.  This  water  is  frequently  raised  to  the  sewer  only, 
the  pump  being  placed  in  a  manhole  opening  and  discharging 
the  water  below  a  temporary  dam  in  the  sewer,  which  prevents 
its  flowing  up  the  sewer  onto  the  work. 

Two  or  more  hand-pumps  are  sometimes  concentrated  at 
one  point  when  the  amount  of  water  is  considerable.  It 
would  in  many  instances  be  cheaper  to  use  a  steam-pump  at 
such  a  place.  Piston,  centrifugal,  and  wrecking  pumps, 
pulsometers,  and  steam-siphons  are  the  steam  appliances  in 
most  common  use  on  sewer  construction.  In  all  of  these  iron 
suction-pipes  are  used,  from  4  to  8  or  10  inches  in  diameter. 
The  piston-pump  is  the  most  economical,  and  adapted  to 
widely  and  rapidly  varying  quantities  of  water,  and  if  the 
water  is  fairly  clean  needs  very  little  attention.  It  cannot, 
however,  pump  gritty  water  without  rapid  deterioration.  The 
centrifugal  pump  can  raise  muddy  or  gritty  water,  chips,  and 
even  small  stones,  its  first  cost  is  less  than  that  of  a  piston- 


PRACTICAL    SEWER    CONSTRUCTION.  311 

pump,  and  it  can  be  repaired  more  cheaply  if  damaged.  It 
requires  a  fairly  constant  and  fixed  quantity  of  water  to  keep 
it  working,  and  is  apt,  especially  when  a  little  worn,  to  give 
trouble  by  losing  its  priming,  when  the  rising  of  water  in  the 
trench  before  it  can  again  be  primed  may  give  trouble.  The 
wrecking-pump  the  author  has  found  to  be  an  excellent  pump 
for  sewerage-work.  It  will  lift  and  discharge  anything  which 
can  pass  through  its  suction-pipe  and  is  extremely  simple  in 
action.  All  these  pumps  must  be  firmly  set  over  or  near  the 
trench  and  their  position  can  be  changed  only  with  consider- 
able labor.  It  is  better  to  set  them  directly  over  the  sump 
and  have  a  suction-pipe  as  short  and  with  as  few  joints  as 
possible. 

The  pulsometer  pumps  muddy  and  gritty  water,  but  is 
not  economical  of  steam  and,  except  in  experienced  hands, 
is  apt  to  act  in  a  provokingly  contrary  manner,  particularly 
after  some  use.  It  has  the  great  advantage,  however,  of 
portability,  being  suspended  by  a  chain,  which  permits  rapid 
changing  of  its  position  without  cessation  of  pumping,  the 
steam  being  conveyed  to  it  through  a  rubber  steam-hose. 
For  pumping  large  quantities  of  water  at  the  point  where 
excavation  is  proceeding  and  where  frequent  change  of  location 
of  pump  and  suction  is  necessary  it  is  perhaps  the  best  contri- 
vance on  the  market.  The  steam-siphon  is  likewise  conve- 
niently portable,  but  is  most  extravagant  of  steam  and  is 
hardly  practicable  for  raising  large  quantities  of  water. 

The  pulsometer  and  siphon  are  particularly  adapted  to 
raising  water  from  the  point  where  the  work  is  progressing 
with  the  least  interference  therewith.  Piston,  centrifugal, 
and  wrecking  pumps  are  best  used  at  a  distance  from  the  work 
to  lift  water  which  has  flowed  to  them  through  sub-drains  or 
the  sewer,  although  they  are  often  used  at  the  work  when  the 
same  sump  can  be  used  for  two  or  three  days  at  a  time. 

All  suction-pipe  on  either  steam-  or  hand-pumps  should  be 
provided  with  a  strainer  at  the  bottom,  and  the  centrifugal 


312  SEWERAGE. 

requires  a  foot-valve,  which  it  is  also  well  to  supply  for  the 
other  steam- pumps.  If  a  chip  or  other  obstacle  should  hold 
this  valve  open  and  prevent  priming  the  suction  a  shovelful 
of  stable  manure  dropped  into  the  suction-pipe  will  in  many 
cases  enable  the  valve  to  hold  its  priming. 

All  parts  of  the  machinery  should  be  readily  accessible, 
particularly  any  valves,  and  wrenches  and  screw-drivers,  pack- 
ing, oil,  waste,  duplicate  nuts,  washers,  etc.,  should  be  kept 
constantly  at  hand.  A  cessation  of  pumping  for  15  minutes 
may  permit  the  water  to  drive  the  workmen  from  the  trench, 
to  soften  the  banks  and  endanger  the  sheathing,  ruin  the 
green  masonry,  stop  up  sub-drains,  or  do  other  serious 
damage.  A  good,  intelligent,  careful  stationary  engineer  is 
a  necessity  on  such  work. 

The  water  raised  from  the  trench  should  not  be  discharged 
upon  the  ground  near  the  sewer,  unless  the  street  has  imper- 
vious pavement,  as  it  might  soak  back  into  the  trench  and  be 
pumped  over  and  over  again.  It  may  be  carried  to  the 
nearest  watercourse  or  sewer-inlet  or  manhole  along  the 
gutters,  in  wooden  troughs,  or  in  sewer-pipe  temporarily  laid 
on  the  ground  with  joints  tightly  calked  with  oakum  or  clay. 

It  usually  pays  to  keep  the  water  pumped  down  all  night, 
even  if  there  is  no  work  to  be  damaged  by  its  rising,  as  this 
would  again  fill  the  surrounding  ground  with  water,  which 
might  not  drain  out  for  several  hours  after  pumping  began  the 
next  day.  It  may  be  well  to  whitewash  one  or  two  sheath- 
ing-plank  down  to  the  trench  bottom  each  evening,  which 
will  give  evidence  next  day  if  the  engineer  has  not  kept  the 
water  down.  A  shelter  should  be  built  in  front  of  the  boiler 
to  protect  the  engineer  from  storms. 

While  using  a  diaphragm-pump  always  have  spare  dia- 
phragms and  an  extra  length  of  suction-hose  on  hand. 

Moving  a  pump  and  boiler  often  costs  more  indirectly  in 
interference  with  the  work  than  the  immediate  expense  comes 


PRACTICAL   SEWER    CONSTRUCTION.  313 

to.  In  general  every  effort  should  be  made  to  set  the  pump 
in  such  a  place  and  manner  that  it  need  not  soon  be  moved. 
Be  sure  to  have  the  blocking  under  it  solid,  to  prevent  the 
suction-pipe  joints  from  working  loose  or  breaking. 

ART.  73.     HANDLING  WET  AND   QUICKSAND  TRENCHES. 

If  excavation  is  in  good  material  and  of  comparatively 
uniform  depth  a  sewer  gang  once  organized  should  move  along 
at  a  uniform  rate  of  300  or  400  feet  a  day  for  small  pipe 
sewers,  25  to  200  feet  for  brick  or  concrete  ones,  and  with  little  but 
routine  work  for  the  foreman.  If  genuine  quicksand  is  en- 
countered, however,  every  foot  of  progress  must  be  fought 
for  with  unflagging  energy,  pluck,  and  intelligence.  In 
ordinary  wet  trenches  the  difficulty,  while  not  usually  so 
great,  is  sometimes  considerable.  In  both  an  intelligent 
adapting  of  the  work  to  every  new  exigency  is  necessary. 

Water  is  met  with  as  springs  in  the  trench  or  as  a  general 
exuding  from  all  the  ground.  The  former  can  easily  be 
managed  by  catching  the  water  at  its  point  of  exit  and  pump- 
ing it  away.  If  it  enters  from  the  bottom  of  the  trench  it  can 
sometimes  be  caught  in  a  trough  and  led  back  and  discharged 
into  either  the  completed  sewer  or  into  a  tub  in  which  the 
suction-pipe  of  a  pump  is  placed.  It  is  absolutely  useless  to 
attempt  to  stop  the  water  from  coming  out  of  the  ground; 
the  endeavor  must  be  to  handle  it  after  it  gets  out.  In  the 
case  of  a  spring  in  a  brick-sewer  trench  a  method  often  advan- 
tageous is  to  build  into  the  brick-work  opposite  the  spring  a 
small  pipe,  2  to  4  inches  diameter,  through  which  the  water 
can  enter  the  sewer,  and  to  conduct  it  back  from  there  to  the 
finished  sewer  in  a  trough.  This  pipe  can  be  plugged  after 
the  masonry  is  thoroughly  set,  but  might  better  be  left  open 
to  drain  the  ground  if  in  a  storm-sewer,  or  if  in  a  combined 
sewer  and  well  above  the  line  of  flow  of  house-sewage.  This 
pipe  can,  in  many  cases,  be  so  driven  into  the  bank  at  the  spring 
that  the  water  will  flow  through  it  and  the  trough  be  set  before  the 
brick-work  is  begun  at  that  point,  the  trench  being  thus  left  dry. 


3H  SEWERAGE. 

If  the  water  does  not  enter  as  a  spring  and  consequently 
cannot  be  caught  in  this  way,  but  if  the  ground  is  a  gravel 
or  is  not  readily  softened  by  the  water,  an  outer  ring  of  brick 
may  be  built  with  quick-setting  cement,  and  plenty  of  it  in 
beds  as  well  as  joints,  an  occasional  brick  being  left  out  to 
permit  the  water  to  enter  the  sewer-invert,  over  which  it  can 
flow  to  a  sump-hole  ahead  or  through  the  sewer  below.  If 
openings  are  not  thus  left  in  the  brick-work  the  water  will 
force  its  way  through  the  joints.  Plank  should  be  placed  over 
the  brick-work  as  fast  as  it  is  laid  for  the  masons  to  stand 
upon.  This  outer  ring  when  set  may  be  found  uneven  of 
surface,  but  the  joints  will  probably  be  tight.  The  openings 
may  then  be  closed  by  inserting  a  brick  and  calking  the  joints 
with  cloth,  oakum  and  cement,  wooden  wedges,  tea-lead, 
etc.,  or  a  pipe  may  be  inserted  and  the  water  allowed  to  enter 
it  as  described  above.  The  outer  ring  being  thus  made 
water-tight,  the  inner  ones  can  be  built  as  usual,  any  depression 
in  the  outer  ring  being  well  filled  with  mortar.  In  this  and 
in  all  brick-,  stone-,  and  particularly  concrete-work  which  water 
flows  over  while  green  the  surface  can  be  protected  from  wash 
by  spreading  rather  heavy,  strong  brown  wrapping-paper  over 
it.  Cheap  wood-pulp  paper  is  of  little  use.  The  paper  when 
wet  will  cling  to  the  masonry,  remaining  intact  for  days  and 
even  weeks. 

In  building  concrete  sewers  a  bottomless  trough,  slightly 
larger  at  top  than  at  bottom,  may  be  set  in  the  bottom  of  the 
trench  before  any  concrete  is  placed  in  that  section,  being  just 
the  thickness  of  the  invert  in  height.  The  invert  form  rests  on 
this,  and  the  concrete  is  placed  as  usual.  When  the  form  is 
removed  the  trough  also  is  removed  and  the  channel  which  is 
left  is  filled  with  concrete,  or  with  an  outside  course  of  brick  which 
is  finally  made  tight  as  described  above,  and  the  upper  part  of 
the  channel  is  then  filled  with  concrete. 

If  the  ground  is  running  sand  or  soft  it  will  generally  be 
desirable  to  build  a  concrete  or  brick  sewer  on  a  platform,  filling 


PRACTICAL    SEWER    CONSTRUCTION.  315 

the  haunches  between  platform  and  sheathing  with  the  same  kind 
of  material.  The  sub-drain  may  then  be  placed  on  the  platform 
along  each  side,  but  generally  it  is  better  under  the  platform. 

Another  plan  is  to  dig  a  sump-hole  ij  to  3  feet  deep  in 
the  centre  of  the  section  of  invert  under  construction,  and 
keep  the  water  lowered  in  this  by  a  pump  until  the  brick-work 
is  completed  and  set  everywhere  except  over  the  sump.  If 
the  ground  is  very  porous  the  water  will  all  flow  to  the  sump 
and  leave  the  trench  dry  for  several  feet  in  each  direction. 
When  the  surrounding  masonry  has  set  the  suction-pipe  is 
removed  from  the  sump-hole,  and  this  is  filled  with  sand, 
gravel,  or  concrete,  thoroughly  rammed.  The  remaining 
brick-work  is  then  laid,  with  or  without  a  pipe  through  it,  as 
described  above. 

A  better  plan  is  to  use  sub-drain  pipe,  discharging  into  a 
sump,  which  is  to  be  pumped  if  there  is  no  outlet  for  it  or  if 
the  drain  below  is  too  small  to  carry  all  the  water.  A  disad- 
vantage in  this  connection  of  building  either  brick  or  pipe 
sewers  down  instead  of  up  grade  is  that  the  water  cannot  be 
run  away  through  the  sewer  or  sub-drain,  whether  it  be 
pumped  or  not,  and  although  it  drains  away  from  the  work  it 
is  only  to  soak  into  the  ground  ahead  and  make  that  all  the 
wetter,  besides  the  fact  that  it  is  accumulated  where  the 
excavation  is  in  progress.  Not  only  this,  but  the  ditch  acts 
as  a  drain  to  conduct  down  to  the  work  water  from  all  the 
territory  above  which  has  been  passed  through,  the  use  of  a 
sub-drain  adding  greatly  to  this  amount.  If  the  trench  be 
dug  up  hill  it  will  while  advancing  tend  to  drain  out  the 
ground  ahead  and  a  trench  may  be  found  dry  which  would  be 
wet  if  approached  from  above.  In  some  instances  where  a 
trench  has  been  extended  up  to  ground  which  seemed  hope- 
lessly wet,  and  the  trench  thoroughly  braced  and  left  open  for 
a  week  or  two,  the  excavation  was  then  resumed  without  diffi- 
culty, the  ground  being  found  comparatively  dry. 

This  fact,  that  wet  ground  will  in  many  cases  drain  out  if 


316  SEWERAGE. 

an  outlet  be  provided,  may  be  taken  advantage  of  in  several 
ways.  For  instance,  if  beneath  the  wet  porous  soil,  but 
above  the  sewer  grade,  is  a  stratum  of  clay  the  trench  may 
be  carried  down  to  this,  braced,  and  allowed  to  drain  out, 
when  the  clay  can  be  readily  cut  out  dry  instead  of  as  a  thick, 
sticky  paste  which  mires  the  feet  and  will  not  leave  the 
shovel.  Quicksand  can  sometimes  be  dried  out  if  the  water 
be  given  an  outlet  and  sufficient  time  allowed.  It  will  then  be 
almost  as  hard  as  rock,  but  much  easier  to  handle  than  in  its 
quick  state. 

If  sewer  construction  is  in  the  shape  of  an  extension  from 
a  line  already  in  use  into  which  the  water  must  not  be  run,  or 
if  it  is  carried  on  in  sections  which  have  no  outlet,  a  pumping- 
station  can  take  the  place  of  an  outlet,  or  a  ditch  can  some- 
times be  carried  to  a  watercourse  lying  below  the  sewer.  The 
latter  is  always  the  better  plan  if  not  too  expensive,  as  there 
is  then  no  danger  from  broken  or  disordered  pumps.  But  the 
ditch  must  be  above  the  reach  of  any  probable  flood  in  the  stream 
into  which  it  discharges. 

A  plan  used  with  success  on  the  Metropolitan  Sewerage 
System  (Boston),  and  since  then  at  a  number  of  other  places, 
is  to  drive  2-  or  2 J-inch  pipes  by  water-jet  on  one  or  both  sides  of 
the  trench,  10  to  15  feet  apart  and  to  a  point  2  or  3  feet  below  the 
bottom  of  the  sewer,  and,  by  connecting  a  number  of  them  to  a 
6-inch  suction-main  and  pumping  on  them  for  a  few  days,  lower 
the  ground-water  before  the  excavation  reaches  this  point,  and 
keep  it  lowered  until  the  work  here  is  completed.  If  the 
trench  is  less  than  about  20  feet  deep  the  pipes  may  be  driven 
outside  the  trench,  but  if  more  it  will  probably  be  necessary 
to  put  them  and  the  pump  inside  the  sheathing  at  a  distance 
of  not  more  than  20  feet  from  the  bottom,  although  they  may 
be  in  the  way  there.  The  sinking  of  such  tubes  in  Newton, 
Mass.,  cost  from  8  to  50  cents  per  foot. 

In  laying  pipe  sewers  in  wet  trenches  much  of  the  above 
is  not  applicable.  The  best  method  for  such  work  is  the  use 


PRACTICAL    SEWER    CONSTRUCTION. 


of  sub-drains.  When  the  ground  is  not  excessively  wet  the 
trench  is  then  dry  for  the  laying  of  the  sewer-pipe.  But 
where  there  is  a  large  flow  of  underground  water  it  may  be 
impossible  for  it  to  reach  the  sub-drain,  through  the  overlying 
gravel  or  stone,  as  rapidly  as  it  enters  the  trench.  Frequent 
sumps  must  then  be  provided,  with  a  pump  at  each,  there 
being  always  one  only  a  few  feet  ahead  of  the  sewer.  If 
water  still  flows  over  the  trench  bottom  to  the  sump  it  may 
be  necessary  to  lay  the  sewer  in  concrete.  In  fact  this  is 
always  desirable,  though  expensive,  in  wet  trenches  or  where 
sub-drains  are  used.  In  using  concrete  it  should  be  placed 
and  rammed  in  the  trench  and 
the  pipe  bedded  in  it  before  it 
sets.  The  concrete  may  be 
brought  up  only  a  short  distance 
above  the  invert  of  the  pipe, 
being  sloped  down  toward  the 
sheathing  and  forming  a  gutter 
on  each  side  in  which  the  water 
may  run  to  the  nearest  manhole 
or  sump.  If  this  flow  is  consid- 
erable, plank  or  boards  or  heavy 
paper  may  be  laid  on  the  con- 
crete to  protect  it  from  wash. 
The  rest  of  the  sewer-joint  may 
be  made  in  the  ordinary  way.  It 

is  better,  however,  to  also  carry  the  concrete  entirely  over  the 
sewer  at  the  joints  after  a  stretch  between  manholes  is  com- 
pleted and  the  side  gutters  are  no  longer  needed. 

Water  should  never  be  allowed  to  stand  in  bell-holes  after 
a  pipe  is  cemented.  If  liable  to,  the  bell-hole  should  be  filled 
with  cement  or  concrete,  or  at  least  with  sand  or  gravel  well 
tamped.  No  water  should  be  allowed  to  run  through  a  sewer 
until  the  cement  is  fully  set.  Particular  attention  should  be 
paid  to  branches  and  slants  in  wet  trenches  to  see  that  they 


FIG.  27. — SEWER-PIPE  LAID  IN 
CONCRETE. 


318  SEWERAGE. 

are  tightly  sealed.  It  is  an  excellent  plan  to  build  a  dam  at 
each  end  of  a  stretch  of  sewer  in  a  wet  trench,  after  the  sewer 
is  completed  and  cement  set,  and  before  back-filling  above 
the  pipe,  and  allow  the  water  to  stand  upon  it  Leaks  thus 
discovered  are  then  readily  accessible  for  repairs. 

In  moderately  wet  ground  it  is  often  advisable  to  place 
dams  across  the  trench  at  intervals  of  1 5  to  30  feet,  that  there 
may  not  be  so  great  a  stream  continually  flowing  by  the  men 
while  working.  The  head  of  the  trench  being  kept  on  an 
incline,  water  collects  above  each  dam  until  there  are  no  dry 
places  left  in  the  sections  in  which  to  dig,  when  the  dams  are 
opened  in  succession,  beginning  with  the  lowest,  and  the  water 
flows  to  the  sump,  from  which  it  is  pumped.  The  dams  are 
then  closed  and  digging  resumed  immediately  above  each,  the 
laborers  moving  up  the  slope  as  the  water  rises  above  each  dam. 

The  combination  of  water  with  a  particular  kind  of  sand 
produces  what  is  called  quicksand.  Any  object  resting  upon 
this  sinks  slowly  into  it  until  it  has  displaced  its  own  weight 
of  sand.  But  a  pick  can  hardly  be  driven  into  quicksand 
which  has  not  been  disturbed.  The  sand  is  very  fine  and  is 
easily  stirred  up  and  carried  by  running  water,  but  will 
quickly  settle  into  a  tough,  compact  mass  which,  if  allowed 
to  dry  out,  will  become  almost  as  hard  as  soft  sandstone. 
Quicksand  is  semi-fluid  and  will  run  under  sheathing  unless  it 
be  driven  to  a  considerable  distance  below  the  bottom  of  the 
trench.  If  the  influx  is  not  cut  off  by  deep  sheathing,  by  the 
time  the  excavation  is  2  or  3  feet  into  quicksand  a  point  is 
reached  beyond  which  no  headway  can  be  made,  the  bottom 
remaining  at  the  same  level  however  much  be  taken  out  of  it. 
After  a  time  the  cavities  behind  the  sheathing,  caused  by  the 
flowing  of  the  quicksand  from  there  into  the  trench,  permit 
the  ground-surface  to  settle  or  to  drop  entirely,  and  the 
sheathing,  relieved  of  outside  pressure  and  friction,  is  apt  to 
completely  collapse.  If  there  is  any  possibility  that  such  a 
cavity  is  forming  all  braces  should  be  nailed  to  the  rangers 


PRACTICAL    SEWER    CONSTRUCTION. 


and  tied  together  by  cross-bracing,  and  outside  rangers  braced 
against  the  sheathing  from  the,  curb  or  other  points  well  back 
of  the  trench.  If  there  is  more  than  one  course  of  sheathing 
the  plank  in  the  upper  ones  should  be  nailed  to  the  rangers. 
If  the  ground-surface  should  fall  into  the  cavity  thus  made 
sod,  straw,  brush,  etc.,  should  be  thrown  against  the  sheath- 
ing, which  will  stop  the  quicksand  from  flowing  into  the 
trench.  The  entire  cavity  should  then  be  filled  with  earth, 
ashes,  or  some  good  filling  material.  It  is  in  most  instances 
well,  if  the  condition  is  such  as  is  shown  in  Fig.  28,  to  remove 


Quick 


Sand 


FIG.  28. — SHEATHING  A  BADLY  CAVED  TRENCH. 

a  plank  or  two  here  and  there  from  the  upper  course  of 
sheathing  and  throw  into  the  cavity  sods  or  straw,  and  then, 
after  bracing  the  sheathing  as  above  described,  to  break  down 
the  top  soil  and  fill  the  cavity  with  good  earth.  Fig.  28  is 
no  exaggeration  of  conditions  sometimes  occurring  in  quick- 
sand. A  preventative,  which  is  usually  effective,  is  to  keep 
several  men  continually  driving  the  sheathing  with  light 
mauls,  or  better  still  keep  steam-hammer  pile-drivers  at  work, 
so  that  the  bottom  of  the  sheathing  is  continually  maintained 
a  foot  or  two  below  the  bottom  of  the  trench.  This  is  a  pre- 
caution which  should  never  be  neglected. 


320  SEWERAGE. 

One  effect  of  the  formation  of  the  cavities  described  is 
that  the  top  earth  tends  more  than  ever  to  fall  towards  the 
trench,  and  consequently  the  strain  on  rangers  and  braces 
becomes  severe.  It  is  better  to  multiply  the  number  of 
rangers  than  that  of  the  braces  to  each  ranger,  as  the  trench 
is  then  less  obstructed  for  lowering  materials. 

Quicksand  has  usually  only  a  little  water  flowing*  through 
it,  but  that  little  should  be  handled  by  pump  if  possible  and 
not  allowed  to  run  into  the  sewer  or  sub-drain,  the  result  of 
which  would  be  the  rapid  choking  of  the  drain,  or  of  the 
sewer  if  small,  by  quicksand.-  Quicksand  should  not  be 
thrown  directly  back  upon  the  finished  sewer,  as  its  angle  of 
stability  is  exceedingly  small,  and  it  is  apt  to  run  forward  to 
the  upper  end  of  the  sewer,  either  requiring  to  be  handled  over 
again  or  flowing  into  the  mouth  of  the  pipe.  If  thrown  upon 
the  bank  and  dried  out,  however,  it  becomes  very  hard  and 
expensive  to  shovel  back.  It  is  probably  better  to  back-fill 
with  it  immediately  at  some  distance  from  the  sewer  under 
construction,  carrying  it  there  by  excavating-machinery  or  in 
wheelbarrows,  or  to  let  it  partly  dry  upon  the  bank  before 
throwing  it  back.  It  is  well  to  have  a  few  short  plank  nailed 
together  to  form  platforms  which  can  be  placed  in  the  trench 
bottom  for  the  men  to  stand  upon,  as  otherwise  they  will  lose 
much  time  digging  themselves  and  each  other  out.  The 
length  of  open  trench  should  be  kept  short  and  the  men 
worked  as  close  together  as  practicable,  and  sub-drain  with  its 
gravel  and  platform  put  in  and  sewer  laid  as  rapidly  as  possi- 
ble. Even  then  the  danger  is  not  over,  as  the  structure  is 
liable  to  be  raised  out  of  place  by  inflowing  quicksand.  A 
pipe  sewer  which  had  been  laid  in  quicksand  and  covered  with 
the  same  material  as  back-filling  has  been  known  to  rise  more 
than  3  feet  overnight,  practically  floating  to  the  surface  of 
the  quicksand.  To  prevent  this  a  plank  may  be  laid  over  the 
sewer  and  braced  down  from  the  sheathing  and  the  pipe  thus 
held  in  place. 


PRACTICAL    SEWER    CONSTRUCTION.  321 

In  the  case  of  a  brick  sewer  the  platform  should  generally 
be  set  upon  piles  (which  can  best  be  driven  by  the  water-jet) 
and  immediately  loaded  with  brick  or  stone  which  is  to  be 
used  in  the  construction.  It  is  advisable  in  most  cases  of 
large  sewers  built  in  quicksand  to  place  close  sheathing  across 
the  trench,  15  to  30  feet  ahead  of  the  completed  sewer,  mak- 
ing a  coffer-dam,  inside  of  which  the  next  section  of  sewer 
is  built.  Meantime  other  cross-sheathing,  15  to  30  feet  still 
further  ahead  of  the  last,  is  being  driven,  together  with 
the  side  sheathing,  and  the  coffer-dam  thus  formed  excavated. 
When  this  is  down  to  grade  and  the  foundation  in,  the  cross- 
sheathing  just  ahead  of  the  completed  sewer  is  removed  and 
the  sewer  continued  into  the  next  section  of  trench.  In  each 
of  these  coffer-dams,  usually  in  one  corner,  is  a  sump  from 
which  the  water  is  kept  pumped.  A  pail  or  barrel  should  be 
used  in  every  sump  in  quicksand  and  the  sand  kept  dug  away 
from  around  it,  as  it  is  very  apt  to  reach  and  stop  the  suction- 
pipe,  from  which  it  is  difficult  to  remove  it.  Gravel  or  fine 
broken  stone  may  be  placed  around  the  barrel  and  carried  a 
few  inches  above  it  to  prevent  the  sand  reaching  it. 

Laying  pipe  sewers  in  quicksand  may  be  even  more  diffi- 
cult than  building  brick  ones.  If  a  platform  foundation  is 
used  there  is  not  sufficient  weight  in  the  pipe  to  hold  it  down 
and  it  must  be  strongly  built  and  braced  down  from  the 
sheathing.  The  following  plan  has  worked  well:  A  sill  of 
4X6  timber  is  laid  near  each  side  of  the  trench,  which  has 
been  brought  as  near  as  possible  to  grade,  and  a  short  piece 
of  plank  is  stood  upon  it  near  one  end.  Two  or  more  men 
then  stand  upon  the  sill  near  this  end  and  work  it  down  to  the 
necessary  depth,  when  the  upright  is  nailed  to  a  brace  or 
ranger  and  the  sill  at  this  point  thus  held  down  to  place.  The 
other  end  is  then  worked  to  place  and  similarly  braced  and 
the  other  sill  treated  likewise.  By  this  time  the  sand  is  prob- 
ably several  inches  deep  over  both  sills.  Cross-planking  for 
the  platform  having  been  sawed  to  length — the  closer  they  fit 


322  SEWERAGE. 

between  the  sheathing  the  better — one  at  a  time  a  place  is 
cleaned  for  them  and  they  are  nailed  to  the  sills  with  close 
joints.  Good  material  is  then  placed  on  this  platform  and  the 
pipe  laid  thereon  and  the  same  material  immediately  back- 
filled around  and  above  it.  When  the  pipe  has  been  laid  to 
the  end  of  the  platform  it  should  be  tightly  plugged,  if  the 
next  platform  is  not  ready  to  continue  laying  (as  it  probably 
will  not  be),  to  keep  out  the  quicksand,  which  may  rise  above 
the  pipe-invert  before  the  laying  is  continued. 

Another  plan  for  laying  sewer-pipe,  and  an  excellent 
one  for  sub-drains,  in  quicksand  is  as  follows:  Two  planks, 
each  about  6  feet  long,  are  stood  upon  edge  a  sufficient  dis- 
tance apart  to  permit  laying  between  them  the  sewer-pipe,  or 
drain-pipe  and  required  broken  stone,  and  a  strip  of  wood  is 
nailed  across  their  tops  at  each  end.  The  other  edges  are 
then  turned  up  and  similarly  treated,  a  bottomless  trough 
being  thus  formed.  A  loose  bottom  is  provided  to  fit  it, 
usually  in  two  or  three  pieces.  The  bottomless  trough  is 
then  placed  in  the  trench  with  the  plank  on  edge  and  worked 
down  into  the  quicksand  until  to  the  necessary  depth  and  in 
the  correct  line,  and  is  braced  down  from  the  sheathing.  The 
sand  is  then  shovelled  out  of  this  and  the  bottom  planks  put 
in,  one  at  a  time,  the  men  standing  on  the  trough  bottom 
until  all  the  planks  are  in  and  secured,  which  is  effected  by 
placing  a  cleat  across  the  bottom  at  each  end  and  fastening  it 
to  the  sides  of  the  trough.  The  sewer,  or  sub-drain  and 
broken  stone,  are  laid  in  this  and  good  material  is  packed 
around  and  over  the  sewer.  This  method  is  also  adapted  to 
dry  running  sand,  where  the  trough  can  generally  be  used 
without  a  bottom. 

Another  method  sometimes  employed  is  to  excavate  the 
quicksand  in  short  sections  somewhat  below  the  pipe-level 
and  refill  it  with  cinders,  or  spread  burlap  over  the  bottom 
and  cover  it  with  gravel,  on  which  the  sub-drain  or  sewer  is  laid* 


PRACTICAL    SEWER    CONSTRUCTION.  323 

Still  another  plan  is  to  drive  tubes  a  few  feet  apart  through- 
out the  entire  trench,  a  few  at  a  time,  their  bottoms  being  all 
about  a  foot  or  two  below  the  pipe  grade,  and  inject  cement 
and  water  under  pressure,  the  cement  filling  the  interstices  of 
the  surrounding  sand  and  forming  an  artificial  stone,  which 
prevents  the  quicksand  from  rising.  The  pipes  are  then 
removed  and  the  trench  excavated.  This  process  is  patented 
and  expensive. 

In  laying  sub-drains  through  wet  soils,  particularly  wet 
sand,  a  great  deal  of  annoyance  and  expense  will  almost 
surely  be  incurred  if  some  plan  is  not  carried  out  for  keeping 
the  pipe  free  from  deposits,  which  will  form  from  the  dirty 
water  flowing  into  the  end  of  the  pipe.  It  is  an  excellent 
plan  to  keep  a  rope  drawn  through  at  least  600  feet  of  the 
pipe,  the  end  being  drawn  forward  through  each  length  as  it 
is  laid.  At  intervals  of  from  10  minutes  to  half  a  day  the 
rope  should  be  pulled  back  and  forth  to  stir  up  the  deposit 
and  keep  it  moving.  It  is  well  to  knot  up  a  light  chain  and  at 
least  once  a  day  tie  it  firmly  to  the  rope  and  draw  this  through 
the  drain  a  few  times.  If  the  rope  is  neglected  for  too  long  a 
time  it  may  become  imbedded  in  the  deposit  and  require  six 
or  eight  men  or  even  a  team  to  draw  it  through  the  pipe.  It 
should  be  amply  strong  for  this.  When  a  section  between 
manholes  is  completed  the  rope  should  be  left  in  until  the 
next  section  is  completed,  as  a  part  of  the  dirt  flowing  through 
the  upper  will  probably  settle  in  the  lower  section.  The  latter 
should  be  cleaned  at  least  once  every  day.  It  may  be  well, 
if  the  deposits  are  considerable,  to  fasten  to  the  rope  in  the 
lower  section  a  strap  to  which  two  or  three  tapering  tin  cans 
are  riveted  (see  Fig.  29).  These  are  drawn  a  little  way  into 
the  pipe,  closed  end  first,  and  then  drawn  back  and  the  dirt 
emptied  from  them.  (If  started  through  the  pipe  mouth  first 
they  would  probably  pile  the  dirt  ahead  of  themselves  into  an 
immovable  mass.)  When  not  in  use  these  should  be  kept  out 


3  24  SEWERAGE. 

of  the  pipe,  as  should  also  the  knotted  chain  above  mentioned, 
to  permit  the  free  passage  of  water. 

It  is  advisable  to  flush  the  drain  with  comparatively  clean 
water  as  often  as  possible.  This  may  be  done  by  catching 
the  ground-water  by  dams,  as  described  above,  and,  when  the 
drain  has  been  laid  up  to  a  dam,  bailing  the  water  rapidly  from 
this  into  the  drain.  Or  a  plank  may  be  set  across  the  trench 
bottom  just  above  the  pipe  and  below  the  dam,  so  as  to  catch  any 
mud  or  stones  which  may  be  washed  down,  but  permit  the  water 


FIG.  29. — APPLIANCE  FOR  CLEANING  SUB-DRAINS. 

to  flow  over;  the  dam  being  then  broken,  but  kept  under  control, 
so  that  it  can  be  closed  if  the  water  become  muddy. 

It  is  well  to  always  keep  in  the  end  of  the  pipe  a  pan  with 
fine  holes  over  the  upper  half  of  its  bottom,  these  holes  forming 
the  only  entrance  for  water  to  the  pipe.  Sticks  and  stones 
are  thus  kept  out  of  the  pipe,  as  well  as  the  water  most  thick 
with  mud.  If  the  water  is  clear  the  perforated  part  of  the 
pan  can  be  placed  at  the  bottom.  These  remarks  refer  par- 
ticularly to  sub-drains,  since  water  should  not  be  permitted 
to  rise  above  the  sewer-invert. 

The  entire  system  of  sub-drains  cannot  be  flushed  too 
often  during  construction — by  hose  from  the  fire-hydrants,  if 
possible.  If  a  drain  is  stopped  up  in  which  there  is  no  rope, 
cr  the  rope  cannot  be  moved,  a  hole  can  sometimes  be  forced 
through  the  obstruction  by  a  line  of  f-inch  or  i-inch  iron 
pipe.  If  this  is  fastened  by  a  special  bushing  or  otherwise  in 
the  end  of  a  hose  and  water  forced  through  it,  it  can  be  driven 
through  in  almost  every  instance  if  the  friction  between  the 
iron  pipe  and  the  deposited  material  does  not  become  too 
great.  If  the  section  in  which  the  stoppage  occurs  is  not  at 
the  incompleted  end  this  plan  cannot  be  adopted ;  but  an  old 


PRACTICAL    SEWER    CONSTRUCTION.  325 

length  of  2  J-inch  hose,  or  at  least  of  garden  hose,  with  no  coupling 
on  one  end  can  be  placed  at  the  end  of  a  line  leading  from  a  fire- 
hydrant  to  and  down  a  manhole,  and  this  end  pushed  into  the  drain; 
when  the  water  is  turned  on  the  hose  can  be  pushed  forward  as  if  it 
were  a  flexible  rod,  and  the  water  from  the  hose  will  wash  the 
obstruction  loose  and  bring  it  back  to  the  manhole,  where  it 
can  be  removed  from  the  sub-drain  well  by  hand,  the  water 
rising  up  and  overflowing  into  the  sewer.  Sand,  gravel,  and 
even  brick-bats  have  been  washed  out  of  drains  by  this 
hydraulic  process. 

When  laying  a  pipe  sewer  the  manhole  is  not  usually  con- 
structed until  the  sewer  has  been  laid  on  each  side  of  it.  In 
quicksand  if  the  trench  is  opened  through  where  the  manhole 
is  to  be  it  will  immediately  fill  up  above  the  sewer.  The  pipe 
must  therefore  be  plugged  at  the  end.  It  is,  for  this  and 
other  reasons,  often  desirable  in  quicksand  to  build  the  man- 
hole before  the  sewer  reaches  it,  openings  for  the  sewer  being 
left  in  the  manhole-wall  at  the  proper  points.  The  excavation 
for  the  manhole  must  be  made  in  a  well-hole  close-sheathed 
for  at  least  a  foot  lower  than  the  sewer-invert.  It  will  be 
found  difficult  to  get  the  bottom  in  with  the  ordinary 
methods,  particularly  if  there  is  a  sub-drain  well  to  be  put  in. 
In  such  a  case  the  following  plan  has  been  used  with  success: 
A  12-  or  15-inch  pipe  with  two  T  branches  of  the  size  of  the 
sub-drain,  temporarily  plugged,  is  lowered  into  position  to  act 
as  the  sub-drain  well,  the  bell  being  up  and  the  branches 
being  placed  at  the  grade  of  the  sub-drain,  which  connects  into 
them.  The  manhole  excavation  having  first  been  carried  to 
the  depth  necessary  for  the  foundation,  this  pipe  may  be 
lowered  by  resting  upon  it  with  the  knees  and  digging  the 
sand  from  the  inside,  care  being  taken  to  keep  it  vertical  and 
in  the  proper  position.  When  it  has  reached  the  required 
depth  the  sand  is  scooped  out  a  little  below  its  lower  end  and 
one  or  two  bucketfuls  of  concrete  placed  there  and  rammed 


326  SEWERAGE. 

(see  Plate  X,  Fig.  9).  It  is  well  to  place  a  board  bottom 
inside  the  pipe  on  top  of  the  concrete  and  to  place  brick  on 
this  to  keep  the  concrete  from  being  forced  up,  the  brick 
being  removed  after  the  concrete  sets.  If  necessary  another 
12-  or  15-inch  pipe  is  placed  upright  in  the  hub  of  this  one. 
A  length  or  two  of  drain-pipe  is  fixed  in  each  branch  of  the 
sub-drain  well  in  a  horizontal  position  and  in  the  proper  line 
to  connect  with  the  sub-drain  when  laid,  and  the  manhole 
bottom  is  then  dug  out  to  the  grade  of  the  bottom  of  the 
foundation  and  concrete  placed  there,  before  the  sand  rises,  in 
small  areas  of  8  or  10  feet  at  a  time.  This  is  done  rapidly  and 
the  concrete  loaded  with  brick,  if  necessary,  to  hold  it  down. 
The  concrete  is  placed  last  where  the  channel  comes  and  a 
split-pipe  invert  is  at  once  forced  down  in  it  to  the  proper 
grade,  and  a  straight-edged  plank  placed  on  edge  in  the  invert 
bottom  and  braced  down  from  the  sheathing  to  hold  it  in 
position.  The  formation  of  the  manhole  bottom  is  then  com- 
pleted and  the  walls  built  in  the  usual  way,  sewer-pipe  being 
built  into  the  manhole-walls  where  the  sewers  are  to  enter  it, 
but  loosely  enough  to  permit  of  sliding  the  pipe  out.  The 
sewer  already  laid  or  to  be  laid  is  carried  through  this  opening 
by  a  pipe  cut  to  the  necessary  length,  the  sheathing  having 
been  cut  away  here  to  permit  this. 

Another  plan  is  to  lay  a  plank  foundation  for  the  concrete, 
one  plank  at  a  time  being  put  in  place  and  fastened  to  the 
sheathing,  thus  forming  of  the  whole  a  tight  box,  in  which  the 
manhole  is  built.  Flush-tanks,  inlets,  and  other  appurte- 
nances can  of  course  be  built  in  the  same  way. 

ART.  74.     RIVER-CROSSINGS  AND  OUTLETS. 

For  convenience  of  inspection  and  as  permitting  easier 
maintenance  it  is  best  to  carry  a  sewer  across  a  stream  on  a 
bridge  or  trestle,  keeping  its  invert  at  the  hydraulic  gradient; 


PRACTICAL    SEWER    CONSTRUCTION. 


327 


unless,  of  course,  this  is  below  the  river-bed,  when  the  sewer  will 
occupy  that  position.  Very  often  the  use  of  bridge  or  trestle 
is  impossible  or  prohibitively  expensive,  and  then  an  inverted 
siphon  is  necessary.  In  either  case  the  pipe  will  probably  be 
of  iron  or  wood,  although  a  combination  of  these  with  masonry 
is  sometimes  used.  In  some  instances  it  may  be  better  to 
build  the  siphon  in  tunnel,  when  it  should  be  lined  with  brick 
or  concrete;  or,  as  is  usually  better,  two  or  more  iron  or  wood 
siphon  pipes  may  be  laid  in  the  tunnel,  easy  access  to  them 
being  thus  afforded. 

A  bridge  or  trestle  for  supporting  a  sewer  should  seldom 
be  built  of  wood,  owing  to  the  difficulty  of  providing  for  the 
sewage  when  necessary  renewals  are  being  made.  It  may  in 
some  instances  be  unsafe  to  support  a  sewer  by  an  existing 


FIG.  30.— SEWER  CROSSING  CREEK  ABOVE  WATER. 

bridge,  owing  to  the  great  increase  of  load  thus  brought  upon 
it.  (An  1 8-inch  cast-iron  pipe  flowing  full  of  sewage  will 
weigh  about  225  pounds  per  lineal  foot.)  The  bridge  has  in 
some  cases  been  relieved  of  this  weight  by  constructing  the 
pipe  in  the  form  of  an  arch,  but  this  is  not  generally  advis- 


328  SEWERAGE. 

able.  A  simple  design  for  a  short  span,  as  over  a  creek,  is 
shown  in  Fig.  30;  or  the  pipe  could  be  supported  inside  an 
iron  or  steel  box  girder  of  suitable  size  and  strength.  There 
is  no  danger  of  the  sewage  freezing  unless  the  pipe  is  exposed 
for  a  stretch  of  many  hundred  feet. 

If  the  distance  to  be  crossed  is  more  than  200  or  300  feet 
the  inverted  siphon  will  in  most  cases  be  found  advisable. 
Its  construction  under  water  will  be  similar  to  that  of  river- 
crossings  laid  to  grade,  except  that  in  the  latter  the  most 
advantageous  depth  cannot  be  chosen. 

The  joints  and  pipe  of  subaqueous  siphons  and  other 
sewers  should  be  perfectly  water-tight,  as  it  will  be  necessary 
at  times  to  empty  them  of  sewage  for  inspection.  They  should, 
if  of  small  pipe,  be  laid  to  as  straight  a  line  and  grade  as  any 
part  of  the  system.  If  they  are  sufficiently  large  to  be  entered 
this  is  not  so  important.  They  should  never  be  laid  on  the 
bed  of  the  river,  but  always  beneath  it. 

For  a  sewer  up  to  30  or  36  inches  diameter  cast-iron  pipe 
with  lead  or  hardwood  joints  may  be  used.  The  trench  is 
excavated  at  least  1 8  to  24  inches  wider  than  the  pipe  and  6 
to  12  inches  below  its  grade.  Inside  this  trench  the  pipe  is 
placed  and  suspended  to  grade  or  blocked  up  at  intervals. 
The  joints  are  made  and  concrete  is  placed  under  the  pipe  at 
all  points,  completely  filling  the  trench  for  a  distance  of  2  or 
3  feet  above  the  pipe,  or  to  the  surface  of  the  river-bed,  it  all 
being  thoroughly  rammed.  If  the  concrete  does  not  reach 
the  bed  of  the  river  it  is  well  to  throw  loose  stone  over  and 
along  each  side  of  it. 

If  the  river  is  not  very  deep,  or  a  time  can  be  chosen  when 
such  is  the  case,  it  is  in  many  instances  practicable  to  confine 
it  to  half  the  width  of  the  bed,  at  the  point  of  crossing,  by  an 
earthen  embankment  or  a  coffer-dam  of  timber  or  steel  sheet 
piling,  or  a  combination  of  both,  carried,  just  above  and 
just  below  the  line  of  sewer,  from  above  the  water-line  out 


PRACTICAL    SEWER    CONSTRUCTION.  329 

to  mid-channel,  and  across  the  line  of  sewer  at  mid-stream. 
The  enclosed  space  is  then  pumped  out,  the  trench  dug  and 
sheathed,  the  pipe  and  concrete  put  in  position  and  covered, 
and  the  dam  removed  and  a  similar  one  placed  upon  the  oppo- 
site side  of  the  river,  which  then  flows  over  the  pipe  already 
laid.  In  many  cases  the  best  form  of  dam  for  sewer-crossings 
is  made  by  permitting  the  close  sheathing  of  the  pipe-trench 
to  serve  also  as  a  dam,  extending  above  the  water-surface  and 
backed  by  earth  embankment.  A  brief  statement  of  the 
details  of  carrying  out  this  plan,  which  must,  however,  be 
varied  under  different  conditions,  is  given. 

The  sewer  having  been  laid  up  to  the  river-bank,  a  stout 
stake  is  driven  into  the  river-bed  about  10  feet  from  the  end 
of  this  and  in  line  with  the  down-stream  side  of  the  trench. 
If  necessary  another  is  driven  a  few  feet  lower  down  and  a 
brace  set  from  the  foot  of  this  to  the  top  of  the  former.  A 
frame  of  rangers  and  braces  is  built  upon  the  bank,  of  dimen- 
sions proportioned  for  the  proposed  trench,  and  floated  to 
place  in  line  with  the  trench  already  dug,  the  inner  end  being 
fastened  in  position  against  the  end  of  this  trench  and  the 
outer  being  held  by  the  stake  just  mentioned.  Sheathing  is 
then  driven  on  both  sides  and  the  end  of  this  frame  (the  end 
braces  are  flush  with  the  ends  of  the  rangers)  as  deep  as  is 
possible  before  excavating  is  begun,  and  earth  banked  against 
the  outside  of  it.  The  water  is  then  pumped  out  and  the 
trench  excavated,  the  sheathing  being  kept  driven  as  low  as 
possible,  additional  rangers  and  braces  being  added,  and  the 
excavated  material  thrown  just  outside  of  it.  When  this 
trench  is  at  grade  the  pipe  is  laid,  concrete  put  in,  and  trench 
back-filled  ahead  to  cross-sheathing  which  has  been  set  just 
back  of  the  end  of  the  pipe.  Another  frame  has  meantime 
been  started  just  ahead,  sheathing  driven,  and  outer  embank- 
ment made.  The  cross-sheathing  between  the  new  and  the 
completed  trench  is  drawn  and  the  excavation  continued. 


330  SEWERAGE. 

Cross-sheathing  is  set  at  frequent  intervals  and  the  trench  filled 
up  to  it  to  reduce  the  length  of  open  trench  which  must  be 
kept  free  of  water.  It  is  advisable  not  to  cut  off  the  sheath- 
ing and  remove  the  embankment  at  any  point  until  the  con- 
struction is  completed  to  mid-stream.  It  will  usually  be 
necessary  to  keep  a  pump  going  constantly  during  construc- 
tion. If  the  stream  is  subject  to  freshets  it  may  be  well  to 
set  the  pump  upon  a  flat-boat  anchored  against  the  up-stream 
sheathing.  The  boiler  may  be  kept  upon  this  boat  or  upon 
the  bank,  the  steam-pipe  in  the  latter  case  being  carried  along 
the  sheathing. 

If  the  bed  of  the  river  is  gravelly  considerable  trouble  may 
be  experienced  from  water  leaking  into  the  trench,  the  enter- 
ing water  having  perhaps  passed  into  the  ground  many  feet 
from  the  sheathing.  The  embankment  may  in  such  a  case 
be  carried  as  far  as  possible  from  the  sheathing  on  every  side, 
or  a  thin  layer  of  fine  sand,  sandy  loam,  or  loamy  clay  may  be 
spread  over  the  bottom  for  50  or  75  feet  above  and  below  the 
trench.  Also  manure,  brewery-meal,  etc.,  has  been  used  to 
stop  up  the  pores  of  the  gravel.  Heavy,  closely  woven 
canvas  is  excellent  for  use  in  such  a  case,  in  large  squares  or 
strips  tightly  sewed  together,  one  end  being  fastened  above 
water  against  the  outside  of  the  sheathing,  the  other  anchored 
by  stones  or  other  weights  beyond  the  part  of  the  bed  which 
is  giving  trouble. 

An  excellent  material  for  the  embankments  is  a  puddle  of 
clay,  sand,  and  gravel.  Clay  alone  is  almost  useless.  Fine 
and  coarse  sand  mixed,  with  or  without  gravel,  is  better  than 
clay  alone.  All  sticks,  roots,  and  large  stones  should  be 
removed  from  this  puddle,  and  anything  which,  reaching 
through  the  embankment,  may  offer  a  course  for  the  water. 
If  puddling  material  is  scarce  a  double  row  of  sheet-piling  may 
be  carried  around  the  work,  the  two  rows  being  from  2  to  5 
feet  apart,  braced  together  only  at  the  top,  and  the  space 


PRACTICAL   SEWER    CONSTRUCTION. 


33* 


between  them  filled  with  puddle  well  worked  and  rammed. 
Experience  in  this  class  of  work  is  almost  essential  to  its 
proper  prosecution,  and  written  directions  can  give  only  the 
barest  outlines  for  meeting  but  a  few  of  the  difficulties  which 
may  be  encountered.  Pluck,  foresight,  a  fertility  in  expedi- 
ents, and  common  sense  are  prime  requisites  for  this  work, 
The  water  must  never  for  an  instant  be  allowed  to  get  the 
upper  hand.  If  nothing  else  is  at  hand  the  very  clothes  off 
one's  back  should  be  taken  to  stop  a  leak  temporarily,  should 


FIG.  31. — COFFER-DAM  PUDDLE-WALLS. 

one  unexpectedly  develop  in  an  embankment.  Never  permit 
a  brace,  stick,  or  any  object  to  extend  through  an  embank- 
ment or  puddle-trench  or  -wall.  If  a  trench  surrounded  by 
water  shows  signs  of  collapsing  from  outside  pressure  and  no 
material  for  additional  rangers  and  braces  is  at  hand  the 
trench  can  sometimes  be  saved  by  allowing  water  to  fill  it,  and 
then,  when  the  material  has  been  obtained,  the  water  can  be 
pumped  down  and  bracing  put  in  as  it  lowers.  But  this  is  a 
somewhat  desperate  remedy. 

An  outlet  for  the  Massachusetts  Metropolitan  Sewerage 
System  at  Deer  Island,  in  5  to  10  feet  of  water,  was  built  in 
open  trench,  with  double  sheathing  and  puddle,  as  in  Fig.  31. 
The  sewer  was  6  feet  3^  inches  inside  diameter  and  the  trench 
10  feet  wide  on  the  bottom,  concrete  being  carried  from  about 
i  foot  beneath  the  sewer  to  an  average  of  4  feet  above  it. 
"  The  cost  of  the  trench,  including  coffer-dam,  sheeting  left 


33 2  SEWERAGE. 

in  place,  and  back-filling,  was  $44  per  lineal  foot."  (Engineer- 
ing News,  vol.  XXXI,  page  121.)  The  material  through 
which  the  trench  was  carried  was  sand  and  gravel.  The  work 
was  done  by  day  labor. 

If  the  trench  is  in  rock  or  a  tight  coffer-dam  cannot  be 
made  except  at  great  expense  it  may  be  cheaper  and  better 
to  resort  to  divers.  When  not  in  rock,  however,  the  exca- 
vation of  the  trench  should  be  done  by  a  dredge  or  similar 
appliance  if  possible,  as  divers'  labor  is  very  expensive. 

The  end  of  an  outlet  which  discharges  at  some  distance 
from  the  shore  of  a  stream  or  other  body  of  water  should  be 
so  located  and  designed  that  currents,  tides,  or  storms  cannot 
wash  it  full  of  sand  or  mud,  that  it  cannot  settle  down  into 
the  bottom,  that  it  cannot  be  undermined  by  tides  or  cur- 
rents, and  that  the  sewage  discharged  will  not  settle  in  front 
of  it  and  block  the  outlet.  This  may  be  accomplished  by 
laying  the  sewer  in  a  trench  as  described  above,  and  at  the 
very  end  placing  a  right-angled  bend  pointing  upward  and 
extending  I  to  3  feet  above  the  bottom,  this  upright  pipe 
being  surrounded  with  a  cone-shaped  mass  of  concrete.  Or 
the  end  of  the  sewer  may  be  continued  straight,  but  raised 
gradually  until  the  outlet  is  2  or  3  feet  above  the  bottom,  it 
being  supported  between  two  rows  of  piles  back  to  where  it 
has  2  or  3  feet  of  covering. 

It  is  not  so  necessary  that  an  outlet  pipe  be  straight  in 
line  and  grade  provided  the  grade  continually  falls  at  a  suffi- 
cient rate.  The  use  of  flexible-jointed  iron  pipe,  such  as  is 
frequently  employed  for  water-pipes  at  river-crossings,  may 
often  be  used  for  sewer-outlets.  They  should  be  properly 
protected  by  concrete,  riprap  covering,  or  piling.  For 
furnishing  and  laying  2200  feet  of  24-inch  iron  pipe  with 
Ward  flexible  joints  in  a  bottom  consisting  of  sand,  gravel, 
loose  and  solid  rock,  in  a  trench  having  an  average  depth  of 
4  feet,  the  depth  of  water  at  high  tide  being  1 1£  to  30  feet, 


PRACTICAL   SEWER    CONSTRUCTION.  333 

from  $16.85  per  foot  to  almost  double  this  amount  was  bid  in 
1898.      In  ordinary  river- work  the  cost  should  be  much  less. 

Whenever  subaqueous  work  of  any  considerable  extent  is 
being  done  it  will  be  well  to  have  a  diver's  outfit  on  hand,  as 
its  immediate  use  may  sometimes  effect  a  saving  of  the  work 
from  serious  damage. 

ART.  75.     CROSSING  RAILROADS  AND  CANALS. 

Railroads  should  be  crossed  with  particular  care,  both  that 
no  accident  may  occur  to  either  the  workmen  or  to  passing 
trains,  and  because  of  the  difficulty  of  afterward  repairing 
breaks  or  defects  at  such  points.  This  applies  also  to  sewers 
constructed  in  or  close  to  the  foot  of  railroad  embankments. 

It  is  not  advisable  to  tunnel  under  a  railroad  unless  the 
sewer  runs  quite  deep  and  the  material  is  stable.  A  settling 
of  the  ground  above  the  tunnel  might  prove  disastrous  to 
trains,  and  this  settling  is  extremely  probable,  owing  to  the 
jarring  of  passing  trains.  If  there  is  a  culvert  under  the  road 
through  which  the  sewer  can  be  passed  it  will  often  be  well 
to  take  advantage  of  this,  if  only  a  slight  detour  be  necessary 
in  order  to  do  so. 

If  the  sewer  is  to  pass  under  the  railroad  in  open  cut  each 
rail  should  be  first  supported  by  bridge  timbers,  beams,  or 
iron  rails  placed  under  the  ties  lengthwise  of  the  track  and 
extending  10  to  20  feet  beyond  each  side  of  the  proposed 
trench.  For  a  trench  4  to  6  feet  wide  a  12  X  12  bridge 
timber  25  or  30  feet  long  may  be  used.  A  heavy  steel  rail 
may  be  used  under  the  same  conditions,  but  is  not  generally 
so  stiff.  Each  beam  or  rail  is  placed  in  a  trench  dug  under 
the  ends  of  the  railroad-ties,  just  sufficiently  deep  and  wide 
to  enable  it  to  be  placed  under  the  track-rail.  Hardwood 
plank  are  then  driven  between  this  and  the  ground  and 
wedges  driven  between  each  tie  and  the  beam.  The  trench 


334  SEWERAGE. 

is  then  excavated,  horizontal  sheathing  being  used.  The 
earth  excavated  cannot  be  thrown  upon  the  surface  unless  the 
track  is  temporarily  out  of  use.  It  may  be  handled  by  a 
cable-way  excavator  which  swings  sufficiently  high  to  clear  all 
trains.  The  buckets  for  this  it  will  be  well  to  have  large — 
those  holding  a  cubic  yard  will  do — that  the  number  of  trips 
may  be  lessened.  The  back-filling  can  be  returned  in  the 
same  way  and  should  be  most  thoroughly  tamped. 

Another  method  of  handling  the  earth,  particularly  ap- 
plicable where  there  are  but  two  or  three  tracks,  is  to  throw 
the  excavated  material  beyond  the  outside  track  by  one  or 
two  handlings,  a  space  for  this  having  been  left  clear  of  earth 
by  previous  management.  If  the  trench  is  shallow  and  as 
short  a  length  as  practicable  opened  at  a  time  it  may  even 
be  possible  to  throw  the  excavated  earth  directly  onto  the 
completed  sewer,  but  if  this  is  done  only  a  very  few  men  can 
be  worked  at  this  point. 

After  the  completion  of  the  work  with  thoroughly  tamped 
back-filling  the  trench  should  be  wet  down  every  two  or  three 
days  for  several  weeks,  the  bridge  timbers  or  rails  being  left 
under  the  ties  meantime.  Just  before  each  wetting  earth 
should  be  placed  and  tamped  on  the  filled  trench  to  2  or  3 
inches  above  the  ties.  When  the  trench  shows  no  settlement 
after  a  wetting  down  the  supporting  timbers  or  rails  may  be 
removed. 

For  small  sewers  it  will  be  well  to  use  iron  pipe  with  lead 
joints  for  railroad-crossings,  and  for  large  sewers  the  arch  and 
side  walls  should  be  reinforced  (see  Plate  VI,  Fig.  8).  In 
general  it  is  better  to  place  no  manhole  or  other  appurtenance 
between  or  within  several  feet  of  any  tracks. 

A  trench  in  or  near  a  railroad  embankment  is  subject  to 
the  jarring  of  the  trains  and  needs  to  be  carefully  sheathed. 
This  is  sometimes  difficult  if  the  trench  be  wholly  or  partly 
upon  the  slope  of  the  embankment,  since  there  is  nothing 


PRACTICAL   SEWER    CONSTRUCTION. 


335 


FIG.  32. — SHEATHING  ON  STEEP 
SLOPES. 


opposite  the  upper  ranger  on  the  up-hill  side  against  which 
to  brace  it.  It  will  not  usually  be  practicable  to  place  a  slop- 
ing brace  from  this  to  a  lower  ranger  on  the  opposite  side. 
A  better  plan  would  be  to  brace  the  sheathing  against  posts 
driven  at  intervals  a  little  distance  from  the  lower  side  of  the 
trench  and  throw  all  the  excavated  material  against  this  side. 
The  sheathing  on  the  lower 
side  at  least  should  be  left  in 
and  protruding  a  short  distance 
above  the  ground  after  the  work 
is  completed,  to  prevent  the 
back-filling,  which  should  all 
be  thoroughly  hand-rammed, 
from  being  washed  down  the 
bank  by  rain. 

It  is  not  impossible  to  con- 
struct a  sewer  under  a  canal, 
raceway,  or  other  body  of  water  retained  by  embankments 
without  drawing  off  the  water  or  interfering  with  its  service, 
but  it  is  much  easier  and  safer  to  do  this  work  when,  if  ever, 
the  water  is  out.  The  construction  of  a  system  can  generally 
be  so  managed  that  all  canal-crossings  may  be  made  in  winter 
while  the  water  is  out,  even  if  no  other  part  of  the  system  is 
constructed  at  that  time.  A  raceway  can  in  many  cases  be  car- 
ried over  the  excavation  temporarily  by  a  flume  extending  for 
some  distance  in  each  direction  from  it.  Care  must  be  taken 
to  prevent  the  water  following  the  outside  of  this,  for  which 
purpose  close  sheet-piling  may  be  used  to  advantage,  being 
driven  across  the  raceway  at  each  end  of  the  flume  between  it 
and  the  bank  and  making  a  tight  joint  with  it. 

A  sewer  under  or  near  a  canal  should  be  of  iron  pipe, 
unless  too  large,  when  concrete  may  be  used,  made  very 
rich  and  extra  thick — say  i  part  Portland  cement,  2  parts 
sand,  3  parts  broken  stone,  with  a  5o-per-cent  increase  in 


336  SEWERAGE. 

thickness  over  ordinary  localities.  If  iron  pipe  be  used  cast- 
iron  flanges  made  in  halves  should  be  bolted  on  the  pipe  at 
intervals,  a  thin  lead  strip  being  placed  between  the  pipe  and 
the  flange  casting  to  make  a  water-tight  joint,  or  lead  being 
calked  into  bells  on  the  flange,  as  in  the  case  of  a  sleeve-joint. 
Two  or  three  of  these  flanges  should  be  placed  in  each  em- 
bankment and  others  10  or  15  feet  apart  through  the  canal. 
All  space  under,  around,  and  above  the  pipe 
should  be  thoroughly  filled  with  puddled 
clay,  gravel,  and  sand  carefully  rammed.  If 
clay  cannot  be  had  loam  may  be  used,  free 
from  roots  or  "  muck."  A  good  proportion 
FIG  33  —FLANGE  ^or  tnese  materials  is  I  part  of  clay,  i£  parts 
FOR  PIPE  IN  EM-  of  sand,  and  4  parts  of  gravel,  thoroughly 
BANKMENT.  mixcd  before  placing  in  the  trench.  If  the 
sewer  is  of  concrete,  flanges  of  the  same  material  may  be 
built  around  the  barrel  at  intervals;  or  the  flanges  may  be  of 
stone  masonry,  water-tight,  with  rough  face.  The  flange, 
whether  of  iron,  concrete,  or  stone,  is  better  the  rougher  it 
is.  It  would  be  well  to  imbed  rough  stones  in  the  entire 
outside  of  a  concrete  sewer  under  a  canal  to  prevent  the 
water  following  the  surface  and  creating  a  leak. 

If  the  earth  over  the  sewer  in  the  canal-bed  is  shallow  or 
is  not  absolutely  impervious  there  must  be  sufficient  weight 
in  or  attached  to  the  sewer  to  prevent  it  from  floating  if 
empty.  A  24-inch  iron-pipe  crossing  only  two  or  three  feet 
under  a  canal  has  been  known  to  break  in  two  at  a  joint  and 
a  part  of  it  rise  through  the  thin  earth  covering  into  the  water 
above  on  account  of  the  hydrostatic  pressure  brought  to  bear 
by  seepage-water.  It  must  be  remembered  that  an  empty 
iron  pipe  36  inches  diameter,  for  instance,  to  weigh  as  much 
as  the  displaced  water  must  be  if  inches  thick.  Conse- 
quently the  heavier  weights  of  iron  pipe  should  be  used,  or 
else  they  should  be  weighted  down  with  concrete,  iron  cast- 


PRACTICAL    SEWER   CONSTRUCTION.  337 

ings,  or  in  some  other  way.      It  will  usually  be  found  cheaper 
to  use  the  heavy  pipe. 

If  it  is  necessary  to  pass  a  sewer  under  a  body  of  water  in 
tunnel  this  may  require  the  use  of  compressed  air,  shields, 
etc.,  and  should  not  be  undertaken  without  the  advice  of  an 
expert  in  such  work. 


PART  III. 

MAINTENANCE. 

CHAPTER  XIII. 
HOUSE-CONNECTIONS   AND  -DRAINAGE. 

ART.  76.     NECESSITY  FOR  INTELLIGENT  MAINTENANCE. 

IT  is  the  too  general  rule  that  when  a  city  has  constructed 
a  system  of  sewers  it  considers  its  duty  done,  and  permits  any 
kind  of  connection  to  be  made  with  them,  by  anybody  and  in 
any  way,  and  takes  no  more  thought  of  its  sewers  until  com- 
pelled to  do  so  by  some  obnoxious  conditions  therein.  This 
is  all  totally  wrong,  and  even  criminal.  While  it  is  not 
probable  that  any  well-designed  and  constructed  sewerage 
system  will  ever  become  "  worse  than  no  system  at  all  "  or 
an  "  elongated  cesspool,"  it  will  not  work  at  its  best  efficiency 
and  free  from  objectionable  conditions  if  unattended  to,  any 
more  than  would  any  mechanism. 

Moreover,  a  considerable  expense  has  been  incurred  to 
provide  sanitary  sewerage  for  the  citizens,  but  if  careless  or 
penurious  landlords  or  plumbers  or  ignorant  householders  are 
permitted  to  construct  between  the  sewer  and  the  house,  or 
in  the  latter,  cheap  and  unsanitary  house-connections,  -drains, 
and  plumbing  fixtures  the  health  of  the  citizens  is  endangered 

338 


HOUSE-CONNECTIONS  AND    -DRAIN.AGE.  339 

and  complete  return  for  the  outlay  for  sewers  is  not  received. 
No  dread  of  paternalism  should  interfere  with  the  proper  per- 
formance by  the  city  of  its  manifest  duty  to  require  that  all 
"  sanitary  "  piping  and  fixtures  throughout  the  city  are  sani- 
tary, and  the  sewers  should  be  in  the  charge  of  an  experienced 
officer  who  is  held  responsible  for  their  cleanliness  and 
efficiency. 

The  first  necessity  for  this  oversight  will  come  with  the 
connection  of  the  dwellings  to  the  sewers. 

ART.  77.    REQUIREMENTS  OF  SANITARY  HOUSE-DRAINAGE. 

No  house-connections  should  be  attached  to  a  sewer 
except  in  the  presence  and  under  the  direction  of  a  city 
inspector  and  by  a  party  who  is  under  bond  to  follow  the 
city's  regulations  for  such  work. 

No  house  should  be  allowed  to  connect  with  the  sewer 
until  its  construction  is  entirely  completed,  including  plaster- 
ing and  sanitary  fixtures,  owing  to  the  danger  that  mortar  and 
rubbish  may  otherwise  be  admitted  to  the  sewer. 

No  connection  should  be  made  with  a  sewer  except  at  a 
branch  provided  for  that  purpose.  If  there  should  be  no 
branch  within  a  short  distance  one  may  be  inserted  in  a  brick 
sewer  by  cutting  through  its  wall  and  building  a  slant  firmly 
in  place  or,  in  a  pipe  sewer,  by  removing  a  pipe  and  inserting 
a  branch  pipe  in  its  place.  If  3-foot  lengths  of  pipe  were  laid 
in  the  sewer  a  few  3-foot  lengths  of  branch  pipes  may  be  kept 
on  hand  for  this  purpose.  (Branch  pipes  are  generally  used 
in  2-foot  lengths.)  To  remove  a  pipe  from  a  sewer  it  may  be 
broken  to  pieces  with  a  hammer,  care  being  taken  not  to  crack 
the  adjacent  pipe.  Then,  with  a  cold-chisel  used  with  some 
rare,  the  upper  half  of  the  bell  facing  this  opening  is  broken 
away  and  likewise  the  upper  half  of  the  bell  of  the  branch 
pipe  to  be  inserted.  This  is  then  dropped  into  place  with 


340 


SEWEKAGE. 


the  branch  on  the  wrong  side  and  revolved,  thus  bringing  to 
the  top  of  the  sewer  that  part  of  both  pipes  where  the  bell  is 
wanting.  The  joint  is  then  made,  Portland  cement  being 
substituted  for  the  missing  portions  of  the  bells. 

In  breaking  the  cap  or  plug  out  of  a  sealed  branch  care 
must  be  taken  not  to  break  any  part  of  the  pipe.  If  broken 
the  pipe  should  be  replaced  by  a  new  one,  as  above.  If  the 
branch  is  cracked  it  may  be  left  in,  but  should  be  surrounded 
with  rich  cement  concrete  well  compacted. 

It  is  absolutely  not  permissible  to  cut  a  hole  into  a  pipe 
sewer  and  insert  the  house-connection  therein,  as  it  is  almost 
impossible  to  obtain  a  junction  which  will  not  leak  or  to 
prevent  the  connection-pipe  from  protruding  into  the  sewer. 

The  house-connection  should  never  be  larger  than  the 
branch  which  it  enters,  but  should  preferably  be  smaller.  A 
4-inch  pipe  is  large  enough  for  any  residence  or  small  hotel 
or,  in  general,  for  90  per  cent  of  all  the  buildings  in  most 
cities.  On  a  grade  of  I  :  40  it  should  carry  the  simultaneous 
discharge  of  ten  or  more  water-closet  flushes,  or  that  of  two 
large  bath-tubs  when  emptying  themselves  in  two  minutes. 
This  connection  may  be  of  vitrified  clay  pipe  from  the  sewer 
to  a  point  5  or  6  feet  outside  of  the  cellar  wall.  It  should  be 
laid  to  as  perfect  line  and  grade  as  was  the  sewer  itself,  the 
fall  of  i  :  40  being  the  minimum  allowed  under  any  but 
exceptional  circumstances.  If  a  uniform  grade  from  the  sewer 
to  inside  the  cellar  is  not  obtainable  or  desirable,  or  if  this 
distance  be  more  than  100  feet,  it  is  advisable  to  place  an  in- 
spection-hole at  the  fence-line  or  at  some  other  convenient 
point  (see  Plate  XI,  Fig.  10),  the  grade  and  line  being  straight 
each  way  from  this  to  both  sewer  and  house.  If  the  pipe 
branches  before  reaching  the  house  an  inspection-hole  should 
be  placed  at  the  junction.  The  joints  of  the  house-connection 
should  be  of  cement,  and  it  should  be  of  equally  as  good 
material  as,  and  laid  in  every  way  according  to  the  methods 


HOUSE-CONNECTIONS  AND   -DRAINAGE.  341 

used  for,  the  sewer.  In  made  ground  or  quicksand,  or  where 
trees  are  near  the  pipe,  or  the  latter  passes  near  a  well  or 
cistern,  the  connection  should  be  of  iron  water-  or  gas-pipe 
(not  "  plumbers'  pipe  ")  with  lead  joints. 

From  a  point  5  or  6  feet  outside  the  building  into  and 
through  this  the  main  pipe  should  be  of  iron,  and  should 
extend  vertically  to  and  through  the  roof,  its  upper  end,  down 
to  a  few  feet  below  the  roof,  being  preferably  enlarged  some- 
what. The  top  should  be  at  a  distance  from  any  chimney 
and  above  any  garret  or  other  windows,  and  should  not  be 
furnished  with  a  cowl,  quarter-  or  half-bend,  or  any  other 
device.  All  fixtures  in  the  house  discharge  into  this  pipe, 
the  intersections  being  by  means  of  Y's  and  not  T's. 

So  far  all  authorities  agree.  But  the  general  arrangement 
of  traps  and  ventilation-pipes  is  a  point  upon  which  many  of 
them  differ.  The  principal  point  of  difference  is  as  to 
whether  the  pipe  should  be  furnished  with  a  trap  between  the 
sewer  and  the  vertical  "  soil-pipe."  Most  agree  that  a  trap 
should  be  placed  just  below  each  fixture,  although  a  few 
would  dispense  with  this  and  rely  upon  one  main  trap  only. 
(See  "  The  Single  Trap  System  of  House  Drainage,"  Trans- 
actions Am.  Soc.  Civil  Engineers,  vol.  XXV,  page  394.) 
Some  trap  is  desirable,  if  for  no  other  reason  than  to  prevent 
long  sticks,  bones,  knives  and  forks,  and  other  large  articles 
from  being  carried  to  the  sewer.  Most  sanitarians  would 
ventilate  each  trap  by  connecting  the  end  furthest  from  the 
inlet  with  a  main  vent-pipe  leading  through  the  roof. 

The  object  of  the  main  trap,  which  is  generally  placed 
just  inside  the  cellar  wall,  is  to  exclude  the  air  of  the  sewer 
from  the  building.  As  has  been  previously  stated,  however, 
the  house-connection  and  soil  pipes  are  in  most  cases  much 
more  foul  than  the  sewer,  and  the  danger  lies  in  them  rather 
than  in  the  sewer.  The  vertical  soil-pipe,  on  account  of 
the  spraying  action  of  falling  water,  becomes  fouler  and  is 


342  SEWERAGE. 

more  difficult  to  clean  than  almost  any  other  part  of  a  sewer- 
age system.  Hence  the  author  can  see  little  if  any  advantage 
in  the  presence  of  the  main  trap;  none,  certainly,  if  this  be 
not  vented  on  both  ends  to  prevent  its  seal  being  forced  by 
a  compression  of  the  sewer-air  due  to  a  sudden  discharge  into 
the  sewer  from  a  near-by  connection  or  some  other  cause,  and 
to  prevent  a  forcing  of  the  traps  throughout  the  house  by  the 
compression  of  air  in  the  soil-pipe  caused  by  a  considerable 
flush  of  water  from  a  fixture  on  the  upper  floors;  also  to 
admit  fresh  air  to  the  house-piping.  Many  excellent  authori- 
ties, however,  advise  the  use  of  the  main  trap. 

The  object  of  continuing  the  soil-pipe  through  the  roof  is 
to  allow  the  foul  air  from  below  to  pass  upward  through  it, 
and  there  seems  to  be  little  objection  to  permitting  the  purer 
air  from  the  sewer  to  occasionally  take  the  same  course,  and 
even  perhaps  some  advantage  from  its  diluting  effect. 

Whichever  the  plan  adopted,  if  the  workmanship  and 
material  are  of  the  best  there  is  probably  little  danger  to  be 
feared.  If  vent-pipes  are  used  on  a  main  trap  these  should 
terminate  at  a  distance  of  at  least  10  feet  from  any  window  or 
door,  and  in  such  a  manner  that  they  cannot  be  sealed  by 
dirt,  snow,  ice,  or  frost  collecting  around  the  upper  ends  from 
the  damp  sewer-air. 

Every  trap  and  dead-space  in  water-closets  should  be 
separately  vented  at  the  top  of  the  outer  bend,  the  branch 
vents  connecting  with  the  main  vent,  which  should  be  car- 
ried from  the  lowest  trap  up  through  the  roof.  This  prevents 
siphoning  of  the  traps  by  water  plunging  down  the  soil-pipe 
from  a  higher  closet  or  tub,  and  offers  escape  for  any  foul  air 
forming  in  any  of  the  soil-pipes. 

Authorities  agree  that  water-closets  must  not  be  connected 
directly  with  the  water-supply  pipes,  but  should  be  flushed 
through  an  intermediate  tank  or  tanks  or  similar  appliance; 
that  roof-water  leaders  should  never  be  connected  directly 


HOUSE-CONNECTIONS  AND    -DRAINAGE.  343 

with  the  house-connection  pipe  without  an  intermediate  trap; 
and  that  all  pipes  and  sanitary  fixtures  of  whatever  kind 
should  be  everywhere  accessible  for  examination,  and  should 
not  be  walled  or  even  boxed  in.  The  water-closets  should 
never  be  placed  in  rooms  not  receiving  light  and  air  directly 
from  outdoors,  or  at  the  very  least  from  a  large  air-shaft, 
through  a  window  having  at  least  4  or  5  square  feet  area. 

All  piping  in  and  near  the  house  should  be  of  iron. 
Wrought  iron  with  screw-joints  is  preferable  to  cast  iron. 
The  use  of  lead  pipe  is  not  advisable,  except  in  short  exposed 
lengths,  as  it  may  be  punctured  by  nails  or  gnawed  by  rata 
and  mice,  and  is  apt  to  sag  into  unnecessary  running  traps. 
Where  the  pipe  passes  through  the  cellar  wall  this  should  bes 
arched,  leaving  a  space  of  two  or  three  inches  around  the 
pipe  to  prevent  the  breaking  of  the  pipe  by  a  settlement  of 
either  it  or  the  wall. 

The  house-connection  should  be  suspended  upon  the  side 
walls  after  entering  the  cellar,  and  should  never  be  placed 
under  the  cellar  floor,  unless,  when  this  is  unavoidable,  it  be 
placed  in  a  shallow  trench  having  brick  or  stone  walls  and  with 
a  removable  top  forming  part  of  the  cellar  floor.  The  soil- 
pipe  should  have  only  easy  curves  and  Y's,  no  angles  or  T's 
anywhere. 

Water-closet  tanks  should  discharge  not  less  than  3  gallons 
with  each  flush,  the  pipes  leading  from  these  to  the  closets 
being  not  less  than  ij  or  i£  inches.  No  overflow  from  any 
cistern,  tank,  or  refrigerator  should  discharge  into  any  soil-  or 
waste-pipe,  but  into  a  trapped  sink  or  bowl  connected  there- 
with, the  end  of  the  discharge-pipe  being  at  least  3  inches 
above  the  water  in  said  sink  or  bowl.  There  should  be  no 
wooden  wash-tubs  or  sinks.  Grease-traps,  if  used,  should  be 
cleaned  out  once  a  week.  No  "  bell  trap  "  or  removable 
strainer  should  be  placed  in  sinks  or  tubs.  All  iron  pipes 
used  as  drains  or  soil-pipes  should  be  coated  inside  and  out 


344  SEWERAGE. 

with  coal-tar  varnish,  or  asphalt,  or  better  still  with  enamel. 
A  hand-  and  inspection-hole  should  be  placed  in  the  house- 
connection  just  inside  the  cellar  wall,  and  outside  the  main 
trap  if  one  be  used. 

Every  system  of  house-drains  and  soil-pipes  should  be 
tested  by  water-pressure  to  at  least  10  pounds  before  being 
accepted  or  used.  (See  also  "  House  Drainage  and  Sanitary 
Plumbing,"  and  "  Sanitary  Engineering,"  by  Wm.  P. 
Gerhard.) 

To  insure  that  the  above  requirements  are  met  by  every 
system  of  house-drainage — and  this  shouldbz  insured — regula- 
tions embodying  them,  and  such  others  as  are  thought  desir- 
able, should  be  drawn  up,  and  an  inspector  or  inspectors 
appointed  to  examine  and  approve  of  all  plans  for  house- 
drainage  and  to  see  that  these  are  faithfully  carried  out. 


CHAPTER   XIV. 

SEWER   MAINTENANCE. 

! 

ART.  78.     REQUIREMENTS  OF  PROPER  MAINTENANCE. 

THE  requirements  for  keeping  a  sewerage  system  in  good 
running  order  can  be  concisely  stated  as — preventing  and 
removing  deposits,  and  maintaining  ample  and  safe  ventila- 
tion. 

As  previously  stated,  the  main  dependence  for  preventing 
deposits  is  flushing.  If  a  deposit  remains  for  any  time  it  is 
apt  to  continually  increase  and  become  more  difficult  of 
removal,  and  deposits  should  therefore  be  removed  as  soon  as 
possible  after  forming.  This  the  automatic  flush-tank  is  sup- 
posed to  do  for  800  to  1000  feet  below  it,  but  any  forming 
below  this  limit  will  probably  need  to  be  removed  by  hand- 
flushing  from  a  manhole  or  by  the  use  of  special  appliances. 
If  deposits  continually  form  in  any  one  place  and  are  not 
apparently  occasioned  by  articles  which  should  not  be  intro- 
duced into  the  sewer  it  may  be  advisable  to  place  a  flush-tank 
at  the  head  of  where  such  deposits  form,  at  one  side  of  the 
sewer,  but  connected  with  it  at  a  manhole  or  by  a  Y  branch. 
If  obstructions  are  frequently  formed  at  any  one  place  by  the 
introduction  of  improper  matters,  such  as  ashes,  bones,  etc., 
the  source  of  these  should  be  ascertained  and  the  parties 
responsible  therefor  punished. 

It  should  not  be  taken  for  granted  that  a  sewer  is  working 
properly,  but  the  system  should  be  inspected  once  a  week  or 

345 


346  SEWERAGE. 

at  least  once  a  fortnight.  This  may  require  merely  a  look 
into  each  flush-tank  to  see  that  it  works  properly,  into  each 
inlet  or  catch-basin  to  see  that  it  is  clean  and  the  grating 
unobstructed,  and  into  each  manhole  (the  dirt-pan  being  at 
the  same  time  removed  and  emptied)  to  see  that  the  sewage 
is  flowing  with  sufficient  velocity  and  is  apparently  not 
dammed  back  by  any  deposit  below.  But  during  the  first 
few  months  of  his  service  the  inspector  should  enter  each 
manhole  and  look  through  the  sewer  at  each  inspection  until 
he  becomes  familiar  with  its  condition  of  depth  and  velocity 
of  flow  when  in  good  order.  If  there  are  any  considerable 
odors  observed  about  any  appurtenance  the  cause  should  be 
discovered  and  removed.  This  will  usually  be  a  large  deposit 
or  imperfect  ventilation,  except  in  the  case  of  catch-basins, 
where  it  probably  means  improper  or  infrequent  cleaning. 

The  catch-basins  should  be  cleaned  after  every  rainfall. 
There  is  danger  of  putrefaction  and  objectionable  odor  from 
these  if  this  is  not  done  within  two  or  three  days  after  each 
rain,  but  this  is  almost  impracticable  in  large  cities,  where 
there  are  one  or  two  on  every  corner,  without  the  use  of  an 
enormous  number  of  men  and  carts,  since  each  cart  with  three 
men  will  clean  but  five  to  fifteen  catch-basins  a  day.  As  an 
example  of  what  is  usually  done  in  this  line,  a  large  city  in  New 
England,  which  is  considered  to  have  an  excellent  Department 
of  Public  Works,  during  the  whole  of  one  year  cleaned  its  noo 
catch-basins  an  average  of  1.84  times  each.  It  seems  almost 
impossible  that  these  catch-basins  could  hold  the  heavier 
matter  washed  from  the  streets  during  six  or  seven  months 
(or  if  so  the  small  amount  contributed  by  each  storm  would 
have  done  little  harm  in  the  sewer),  and  the  inference  is 
that  a  large  part  of  this  was  not  held,  but  was  washed 
into  the  sewer;  also  that  the  catch-basins  were  in  an  unsanitary 
condition  a  large  part  of  the  time.  When  so  treated  they  might 
better  be  replaced  with  plain  inlets. 


SEWER   MAINTENANCE.  347 

A  record  should  be  kept  of  all  sewer-inspections,  each  line 
of  sewer  and  each  appurtenance  having  a  record  of  its  own 
showing  when  it  was  inspected,  its  condition,  when  cleaned, 
what  repairs  were  made  to  it,  with  their  nature  and  cost;  of 
the  frequency  of  flushing  or  of  the  discharge  of  each  automatic 
flush-tank;  of  the  location  and  date  of  making  each  house- 
connection,  with  all  details  as  to  route,  size,  and  grade  of 
connection-pipe,  cost,  by  whom  ordered,  by  whom  put  in  (if 
by  private  contractor). 

*  The  house-drainage  is  usually  supposed  to  be,  but  seldom 
is,  looked  after  by  the  owner.  It  is  exceedingly  desirable  to 
have  a  sanitary  inspection  made  of  every  house  by  a  city 
inspector  at  intervals  of  not  more  than  12  months;  but  such 
a  plan  would  hardly  be  favored  by  most  American  communi- 
ties, but  would  be  looked  upon  as  an  impertinence.  It  is  the 
city's  duty,  however,  to  insist  upon  all  owners  and  tenants 
observing  the  sanitary  regulations  as  to  construction  and  use 
of  house-drainage  systems. 

Extensions  of  the  system  should  of  course  be  made  with 
as  much  care  as  were  the  original  sewers,  and  no  alterations 
made  in  the  original  plans  without  a  careful  consideration  of 
their  effect  upon  the  system  as  a  whole. 

ART.  79.     FLUSHING. 

When  automatic  flush-tanks  are  used  they  should  be  in- 
spected at  intervals  to  insure  their  regular  discharging.  The 
most  common  failing  with  siphon-tanks  is  the  trickling  over 
of  the  water  into  the  sewer  as  fast  as  it  enters  the  tank  after 
it  has  once  reached  the  level  of  the  top  of  the  bend.  Under 
this  condition  the  siphon  will  never  flush.  This  trickling  may 
be  due  to  faulty  designing,  but  is  usually  caused  by  a  leaking 
joint  or  blow-hole  in  the  iron  siphon  at  some  point,  which 
must  be  corrected.  The  frequency  of  discharge  is  regulated 


343  SEWERAGE. 

by  the  cock  admitting  the  water.  This  can  be  adjusted  only 
by  actual  trial  with  each  tank.  It  is  a  good  plan  to  have  one 
or  more  registering  reservoir-gauges  for  use  in  the  flush-tanks 
which  will  indicate  the  times  of  discharge.  A  simple  one, 
but  sufficient  for  this  purpose,  can  be  made  with  a  clock- 
works actuating  a  cylinder  on  which  the  height  of  water  is 
constantly  registered  by  a  pen  whose  motion  is  caused  by  the 
rise  and  fall  of  a  float,  a  cord  carrying  the  pen  and  one  from 
the  float  both  passing  over  connected  wheels  of  such  relative 
diameters  that  the  path  of  the  pen  is  but  4  or  5  inches  long.  Such 
an  apparatus  left  for  a  day  or  two  in  a  flush- tank  will  serve  in 
place  of  frequent  visits  to  it,  and  can  be  moved  from  one  to 
another  as  each  is  adjusted  to  the  desired  frequency  of  dis- 
charge. The  waste  of  water  caused  by  flushing  oftener  than 
once  in  eighteen  to  twenty-four  hours  is  not  justified  by  any 
proportionate  advantages. 

Reference  has  already  been  made  (Art.  42)  to  flushing 
directly  from  2-  or  4-inch  branches  led  from  the  water-main 
into  the  flush-tank.  In  using  these  the  valve  is  ordinarily 
opened  to  its  full  extent,  or  so  much  as  is  necessary  to  main- 
tain the  height  of  water  in  the  flush-tank  as  great  as  is  safe 
for  the  tank  or  sewer.  It  may  be  left  open  until  such  time 
as  the  water  flowing  through  the  manholes  below  is  perfectly 
clean.  It  will  be  necessary  to  use  the  most  solid  construction 
in  the  flush-tank  to  resist  the  considerable  force  with  which 
the  water  leaves  the  water-pipe. 

Instead  of  connecting  the  flush-tank  with  the  water-main 
by  a  large  pipe  a  small  one  is  sometimes  used,  and  the  tank 
filled  from  this  after  closing  the  sewer  end,  which  is  then 
opened  and  the  contained  water  allowed  to  flush  the  sewer. 
This  method  takes  much  longer  than  the  previous  one  and 
is  consequently  more  expensive.  In  some  cases  the  flush-tank 
fe  filled  by  hose  from  the  nearest  fire-hydrant. 

In  some  cities  the  water  is  conveyed  to  the  flush-tanks  in 


SEWER   MAINTENANCE.  34? 

carts,  and  either  the  tanks  filled  from  these  and  discharged  by 
hand  as  above,  or  from  the  bottom  of  the  cart  a  large  pipe  or 
canvas  hose  is  lowered  into  the  flush-tank  and  connected  with 
the  end  of  the  sewer,  into  which  the  water  is  discharged  under 
a  head  equal  to  the  elevation  of  the  cart  above  the  sewer. 
In  New  Haven,  Conn.,  such  a  cart  is  used  holding  700  gal- 
lons, in  connection  with  which  an  ovoid  ball  is  passed  down 
the  sewer  to  assist  in  the  cleansing,  its  distance  from  the 
flush-tank  being  regulated  by  an  attached  cord  which  passes 
up  through  the  sewer  and  flushing-pipe  to  the  surface.  These 
carts  are  ordinarily  used  at  manholes  along  the  line  of  the 
sewer  rather  than  at  flush-tanks  proper. 

Flushing,  as  has  been  stated,  is  seldom  effective  for  more 
than  800  to  1000  feet  below  the  point  of  entrance  of  the 
flushing-water.  Hence,  when  automatic  tanks  are  not  used 
at  the  head  of  every  section  of  such  length  which  requires 
flushing,  this  is  performed  at  manholes  wherever  necessary. 
For  this  purpose  outside  water  may  be  introduced  by  carts, 
as  just  described;  or  all  the  openings  in  a  manhole  may  be 
stopped  and  the  manhole  filled  by  hose,  when  the  plug  to  the 
down-stream  opening  is  removed  and  the  sewer  below 
flushed;  or  only  this  opening  is  closed,  and  the  sewage  is 
permitted  to  back  up  in  the  sewer  above,  when  the  plug  is  re- 
moved and  the  sewage  performs  the  flushing.  The  last  method 
is  not  particularly  satisfactory  with  pipe  sewers  in  most 
instances,  since  the  head  obtainable  is  usually  very  small  and 
the  velocity  of  flush  consequently  the  same,  and  if  the  house- 
connection  pipes  are  on  a  flat  grade  the  sewage  may  back  up 
these  to  an  undesirable  height.  Deposits  also  may  form  while 
the  sewage  is  accumulating,  which  will  not  be  removed  by  the 
flush  if  near  the  upper  end  of  the  dammed  sewage,  and  the 
time  required  for  a  sufficient  volume  of  sewage  to  collect  will 
often  be  considerable  and  increases  directly  as  the  necessity 
for  frequent  flushing  in  each  case. 


35°  SEWERAGE, 

The  plugs  used  for  stopping  pipe  and  small  brick  sewers 
may  have  any  of  a  variety  of  forms.  One  design  is  a  simple 
conical  cork-shaped  piece  of  wood  with  heavy  rubber  so  fast- 
ened around  it  as  to  come  between  it  and  the  inside  of  the 
sewer  when  the  plug  is  pushed  into  place  and  make  a  water- 
tight joint.  Another  consists  of  a  solid  centre  of  plank, 
around  the  edge  of  which  is  placed  a  pneumatic  tube  similar 
to  a  bicycle-tire,  which  is  inserted  just  inside  the  sewer  and 
the  tire  inflated  by  a  bicycle-pump.  These  have  ropes 
attached  by  which  to  draw  them  out  of  the  sewer  when  the 
manhole  or  flush-tank  is  full,  the  air  being  first  released  from 
the  tube  of  the  one  last  described. 

Another  plan,  that  of  bracing  a  loose  frame  or  hinged  gate 
against  the  end  of  the  sewer  in  a  manhole,  is  hardly  applicable 
to  properly  constructed  systems,  where  the  manhole-channel 
and  sewer  are  continuous,  but  may  be  used  in  a  flush-tank 
designed  for  the  purpose.  The  cover,  whether  loose  or 
hinged,  may  be  held  in  place  by  a  brace  hinged  at  the  middle 
and  extending  from  the  cover  across  the  flush-tank  to  the 
opposite  wall.  A  rope  is  attached  to  the  hinge  of  the  brace 
and  by  pulling  this  when  the  tank  is  full  the  brace  folds  up 
and  releases  the  cover. 

In  large  sewers  it  is  generally  impracticable  and  unneces- 
sary to  dam  back  the  sewage  higher  than,  or  even  as  high  as, 
the  crown  of  the  sewer,  and  a  dam  one  half  or  two  thirds  the 
height  of  the  sewer  is  sufficient.  This  may  be  made  similar 
to  those  already  described,  but  not  filling  the  entire  bore  of 
the  sewer.  Or  a  4<  pocket  dam  "  may  be  used.  This  con- 
sists of  a  bag  of  tarred  canvas  having  rings  around  its  mouth 
and  a  rope  passing  through  these  long  enough  to  reach 
from  the  sewer  to  the  surface.  Another  rope  is  fastened  to 
the  bottom  of  the  bag.  This  bag  is  filled  with  water  and 
placed  in  the  sewer-invert,  being  held  upright  by  the  rope 
through  the  rings,  and  serves  as  a  dam  to  the  sewage.  When 


SEWER  MAINTENANCE.  351 

this  has  raised  sufficiently  this  rope  is  released,  the  bag 
collapses  and  is  removed  by  the  rope  attached  to  its  bottom. 

In  very  large  sewers  flushing,  if  practised  at  all,  must 
generally  be  done  with  sewage,  on  account  of  the  enormous 
quantity  of  water  required  for  this  purpose.  But  this  prac- 
tice is  not  recommended  where  sufficient  water  can  be 
obtained.  In  the  case  of  storm  or  combined  sewers  advantage 
should  be  taken  of  light  rains  by  damming  up  the  run-off  from 
them  in  the  sewers  and  flushing  with  this  comparatively  clean 
water.  Heavy  storms  of  course  need  no  assistance  in  their 
flushing  effect. 

To  ascertain  the  height  to  which  water  in  a  large  sewer 
has  risen  in  flushing  (or  at  any  other  time,  as  during  storms) 
an  ingenious  method,  employed  at  Omaha,  Neb.,  is  to  drive 
into  the  wall,  2  inches  apart  vertically,  small  iron  rods  with 
the  ends  turned  up,  on  each  of  which  rests  a  cork  with  a  hole 
in  its  bottom,  which  can  be  readily  floated  off  when  reached 
by  the  water.  Upright  whitewashed  sticks  placed  in  the  ver- 
tical diameter  of  the  sewer  have  been  used  for  the  same 
purpose,  but  not  with  perfect  success.  Probably  the  best 
appliance  is  the  Frieze  self-registering  depth-of- water  gauge, 
in  which  a  continuous  record  of  sewage  depth  is  kept  upon  a 
cylinder  revolved  by  clockwork,  the  pen  being  carried  by  a 
vertical  arm  attached  to  another  arm,  one  end  of  which  is  hinged 
and  the  other  carries  a  float  which  floats  upon  the  surface  of  the 
sewage. 

Of  the  various  methods  of  flushing  small  sewers,  a  properly 
regulated  automatic  tank  is  probably  the  least  expensive;  and 
permanent  water  pipes  leading  to  man-holes  require  somewhat 
less  time  than  the  use  of  hose  or  water  carts. 

In  1907,  of  138  cities  of  more  than  30,000  population,  30 
used  automatic  flush  tanks  alone,  78  used  fire  hydrants  or  some 
other  method  of  supplying  water  by  fire  hose,  and  27  used  both 


352  SEWERAGE. 

methods.  New  Haven  was  the  only  one  reporting  the  use  of 
portable  tanks;  and  only  one  of  these  reported  the  use  of  flushing 
valves. 

Cleaning  sewers  in  New  Haven  by  the  water-cart  above 
described  cost  $3  to  $4  per  mile  cleaned.  One  argument 
in  favor  of  hand-flushing  is  that  it  renders  more  probable 
frequent  inspection  of  the  system,  which  will  be  made  at 
the  time  of  flushing;  but  on  the  other  hand  pressure  of  other 
duties  or  carelessness  may  cause  longer  intervals  between 
flushings  than  is  desirable.  As  a  general  rule  automatic 
tanks  should  be  used  on  pipe  sewers  where  there  is  not 
retained  by  the  city  a  constant  force  of  laborers  for  mainte- 
nance of  sewers  and  streets  and  similar  purposes.  In  the  case 
of  large  brick  sewers  it  is  probably  best  to  resort  to  one  of 
the  methods  of  hand-flushing.  For  pipe-sewer  dead-ends  in 
cities  with  a  maintenance  force  automatic  appliances  are 
desirable,  but  are  in  many  instances  not  used.  When  any 
flushing  is  done  elsewhere  than  at  dead-ends  hand-flushing  is 
generally  resorted  to. 

ART.  80.     CLEANING. 

The  purpose  of  flushing  is  to  prevent  deposits,  or  rather 
to  prevent  the  accumulation  and  solidifying  of  deposits.  But 
from  the  insufficiency  or  infrequency  of  flushing  this  object  is 
sometimes  not  attained;  or  obstinate  obstructions  may  be 
formed  by  sticks,  stones,  or  other  matter  which  flushing  is  not 
adequate  to  remove,  and  these  must  be  removed  by  hand  or 
some  other  method.  Catch-basins  must  be  cleaned  by  hand, 
and  this  should  be  done  frequently.  The  manhole  dirt- 
buckets,  also,  should  be  cleaned  at  intervals.  These  last  are 
merely  removed  from  the  manholes  and  dumped  into  a  cart 
or  wheelbarrow. 

The    catch-basins    are    generally    cleaned    by    ordinary 


SEWER    MAINTENANCE. 


353 


shovels,  the  dirt  being  taken  to  the  surface  by  a  bucket  and 
emptied  into  a  cart.  Two  men  and  a  cart  and  horse  suffice 
for  this  work.  In  some  cities,  and  especially  when  the  catch- 
basins  are  small,  the  dirt  is  removed  with  long-  and  heavy- 
handled  hoes,  the  blade  of  the  hoe  being  at  right  angles  to  the 
handle  and  about  8  by  10  inches  in  size.  These  are  used 
from  the  surface  through  the  manhole-opening  or  that  left  by 
removing  the  grating.  Catch-basin  walls  should  be  thoroughly 
cleaned  with  a  hose  and  broom  and  washed  with  a  solution  of 
chloride  of  lime  or  some  deodorizer,  but  this  is  seldom  done. 
The  cost  of  cleaning  a  catch-basin  will  vary  probably  from  50 
cents  to  $2  each,  depending  upon  their  size,  the  frequency  of 
cleaning,  and  other  special  circumstances  or  conditions;  $1.40 
seems  to  be  about  the  average  for  large  cities.  Catch-basins 
at  the  ends  of  siphons  are  difficult  to  clean,  being  in  most 
cases  at  the  bottom  of  a  shaft  containing  many  feet  of  water. 
Long-handled  hoes  may  be  used,  or  the  siphon  may  be  closed 
and  emptied  of  sewage  to  permit  reaching  the  catch-basin. 
An  apparatus  acting  on  the  principle  of  the  steam-siphon  01 
sand-pump  is  used  with  success  in  the  Waltham,  Mass., 
siphon,  emptying  the  catch-basin  or  sump  without  the  siphon 
being  emptied.  The  pipe  B,  Fig. 
34,  is  lowered  into  the  sump  and 
the  nozzle  is  attached  to  a  hose 
from  a  hydrant.  When  the  water 
is  turned  on  the  sand  and  other 
solid  material,  mixed  with  sewage, 
is  sucked  up  through  B  and  dis- 
charged through  A  into  the  sewer, 
from  which  it  is  prevented  from 
returning  by  a  temporary  dam  in  the  end  of  the  sewer. 

Small  sewers  are  cleaned  by  flushing  when  this  is  possible, 
but  in  many  cases  other  means  must  be  resorted  to.  The 
use  of  "  pills  "  is  convenient  where  there  are  no  stones,  sticks, 


FIG.  34. — APPLIANCE  FOR 
CLEANING  SIPHON-SUMP. 


354  SEWERAGE. 

or  other  hard  materials  in  the  sewer.  These  are  round  balls, 
usually  of  wood,  which  are  floated  through  the  sewer  either 
in  the  sewage  or,  if  there  is  not  enough  of  this,  by  flushing 
water.  A  set  of  these  2,  3,  4,  5,  7,  9,  etc.,  inches  in  diameter 
should  be  kept  on  hand.  When  a  sewer  is  to  be  cleaned  the 
smallest  pill  is  floated  through  from  one  manhole  to  the  next, 
where  it  is  caught  by  an  assistant;  the  others  are  then  sent 
through  in  the  order  of  their  sizes  until  all  have  passed 
through  up  to  the  size  one  inch  smaller  than  the  sewer. 
When  any  ball  reaches  a  point  where  the  opening  is  contracted 
by  sediment  to  less  than  its  diameter  the  ball,  which  has 
floated  and  rolled  along  the  top  of  the  sewer,  dams  up  the 
water  until  it  has  sufficient  head  to  force  its  way  under  the 
ball  and  scour  out  the  sediment.  The  ball  rolls  slowly  ahead, 
the  current  washing  away  the  sediment  for  an  inch  or  two 
under  it.  If  there  is  a  lamp-hole  on  the  line  the  ball  may 
bob  up  into  it,  and  a  man  should  be  stationed  there  with  a 
pole  to  push  the  ball  down  and  into  the  sewer  below  the 
lamp-hole.  If  a  stone  or  stick  is  among  the  deposit  the  ball 
may  be  stopped  by  it,  in  which  case  both  stone  and  ball  must 
be  removed  by  another  method.  The  pill  cannot  be  used 
when  the  sewer  is  stopped  entirely  so  that  there  is  no  flow 
through  it.  No  cord  should  be  fastened  to  any  of  these 
round  balls,  as  it  is  liable  to  be  rolled  about  them  and  wedge 
them  in  the  sewer,  catch  in  obstructions,  and  generally  give 
trouble.  Ovoid  balls,  however,  are  sometimes  used  with 
cords  attached.  These  do  not  roll  along  the  top  of  the  sewer, 
and  may  need  to  be  weighted  to  prevent  the  friction  between 
them  and  the  sewer  top  interfering  with  their  motion  ahead. 
In  place  of  the  pill,  particularly  in  sewers  larger  than  12 
or  15  inches,  a  small  carriage  is  sometimes  used  which  travels 
on  wheels  through  the  sewer,  its  front  being  of  such  a  shape 
as  to  almost  fill  its  bore  except  for  an  inch  or  two  at  the 
bottom.  Where  the  sewer  is  not  more  than  3  or  4  feet  in  . 


SEWER    MAINTENANCE.  355 

diameter  the  carriage  is  usually  provided  with  other  wheels 
on  top,  which  are  pressed  against  the  sewer-arch  by  springs. 
This  contrivance  is  hauled  through  the  sewer  by  a  rope,  which 
has  first  been  introduced  into  it  by  floating  through  the  sewer 
a  piece  of  wood  or  cork  carrying  a  cord  to  the  end  of  which 
the  rope  is  attached.  Another  rope  is  fastened  to  the  rear  of 
the  carriage  to  haul  it  back  if  it  strikes  an  immovable  obstruc- 
tion. This  is  a  modification,  and  on  a  small  scale,  of  the 
method  employed  for  cleaning  the  Paris  sewers,  where  a  plank 
form,  similar  in  shape  to  and  but  little  smaller  than  the  sewer- 
invert,  is  carried  by  a  boat  or  wagon  and  lowered  into  the 
sewer  as  far  as  necessary  to  cause  a  scouring  of  the  deposit. 
The  boat  or  car  is  carried  forward  by  the  water  backed  up 
behind  the  scouring-form,  which  is  raised  or  lowered  to  the 
proper  position  by  a  workman  riding  in  the  conveyance. 

These  methods  all  depend  upon  the  scouring  action  of  the 
water  and  presuppose  a  passage  through  the  sewer.  Other 
contrivances  for  cleaning  a  small  sewer  under  such  circum- 


FIG.  35.— DISK  FOR  CLEANING  SEWERS. 

stances  are  based  upon  the  use  of  main  strength  to  haul  the 
material  out.  Probably  the  simplest  is  in  the  shape  of  a 
heavy  plank  disk  to  which  a  rope  is  attached  by  three  short 
light  chains  fastened  to  as  many  bolts  through  the  disk.  One 
of  these  chains  is  attached  at  each  side  and  one  at  the  bottom 
of  the  disk,  and  their  relative  lengths  are  so  arranged  that 
when  all  are  taut  the  top  of  the  disk  will  incline  a  little  away 
from  the  rope.  Upon  the  other  side  of  the  disk,  at  its  top, 
is  fastened  another  rope.  By  the  latter  it  is  pulled  a  short 
distance  into  the  sewer,  lying  flat;  the  other  rope  is  then 
pulled,  when  the  disk  rises  into  an  upright  position  and  scrapes 


356 


SEWERAGE. 


along  the  deposit  in  front  of  it.  It  is  well  not  to  draw  this 
too  far  into  the  sewer  at  once,  but  to  clean  only  a  few  feet  at 
each  trip.  The  dirt  can  be  scraped  to  a  manhole  and  there 
removed  by  buckets.  It*is  awkward  pulling  in  a  manhole 
bottom,  and  it  is  well  to  arrange  a  pulley  in  a  frame,  around 
which  the  rope  passes,  as  also  around  another  pulley  at  the  top 
to  permit  of  a  horizontal  pull.  The  lower  frame  may  consist 
of  two  4  X  6  or  4  X  8  timbers  fastened  to  each  other  parallel 
and  a  short  distance  apart,  between  which  the  pulley  turns  in 
journals  fastened  to  their  under  sides,  these  timbers  being 
braced  against  the  inside  arch  of  the  sewer  and  the  pulley 
being  in  the  centre  of  the  manhole  (see  Fig.  36).  This 
method  can  be  used  where  the  material  is  too  heavy  to  be 
scoured  out  by  pills  or  similar  contrivances,  and  also  as  a 
substitute  for  these. 

In  some  cases  the  sewer  will  be  found  entirely  stopped,  so 
that  no  cord  can  be  got  through  it,  and  an  opening  must  be 
forced  through.  A  rod  of  some  kind  is  used  for  this  purpose. 
Since  none  longer  than  5  feet  can  be  got  into  the  sewer 
through  the  manhole  (unless  it  be  too  flexible  for  efficient 
service)  rods  of  this  length  made  to  joint  together  are  gen- 


tt^>\\^\\^\v>A\VxX\> 

FIG.  36. — METHOD  OF  USING  CLEANING-DISK. 

erally    used.     These    are    sometimes    lengths   of  gas-pipe  with 
screw-couplings,  but  wooden  rods  3  to  5  feet  long,  with  a  peculiar 


SEWER    MAINTENANCE.  357 

hook  or  other  patent  coupling,  are  furnished  by  two  or  three  firms. 
These  are  forced  through  the  obstruction  by  working  them 
back  and  forth  or  even  by  driving  with  a  hammer.  When  an 
opening  is  once  made  it  is  well  to  leave  the  rod  in  it  and 
work  it  a  little  back  and  forth  as  the  sewage  flows  through 
until  the  hole  is  too  large  to  be  in  danger  of  immediately 
stopping  again,  when  a  pill  or  cord  may  be  floated  through 
and  the  cleaning  completed  by  one  of  the  above  methods. 

A  small  sewer  or  sub-drain  may  also  be  cleaned  by  the  use 
of  hose,  as  explained  in  Art.  73. 

In  some  cases  the  obstruction  may  be  so  obstinate  as  to 
necessitate  the  digging  up  of  the  sewer.  Before  doing  this 
its  exact  location  should  be  ascertained  by  pushing  a  rod  to  it 
through  the  sewer  and  measuring  its  length,  or  by  the  use  of 
mirrors,  as  previously  described. 

For  cleaning  house-connections,  sub-drains,  and  other 
small  pipe  which  cannot  be  readily  reached,  garden  hose  is 
excellent,  sufficient  water  being  turned  through  it  to  make  it 
stiff  enough  to  be  pushed  through  the  pipe;  or  rods  may  be 
used,  as  just  described.  Instead  of  a  rod  the  city  of  Waltham, 
Mass.,  has  used  for  these  cases  a  length  of  steam-hose 
filled  with  sand,  a  wooden  plug  being  fastened  in  the  end 
of  it.  This  is  flexible,  but  stiff  enough  for  use  in  a  pipe  only 
3  to  5  inches  in  diameter. 

Even  pipe  sewers  of  1 8  inches  diameter  and  up  can  be 
entered  for  inspection  and  cleaning  by  hand.  It  is  reported 
that  in  Waltham  a  Hungarian  crawled  through  850  feet  of 
15-inch  pipe  running  2\  to  4  inches  deep  with  sewage,  there 
being  in  at  least  one  place  not  over  9  inches  of  clear  space 
above  the  deposits  and  sewage.  The  author  has  seen  a  con- 
tractor crawl  through  200  feet  of  1 8-inch  sewer,  and  it  is 
nothing  unusual  for  a  man  to  pass  through  almost  any  length 
of  24-inch  pipe.  A  large  stone  or  a  stick  wedged  across  the 


358  SEWERAGE. 

sewer  can  frequently  be  removed  in  this  way  and  the  necessity 
for  digging  up  the  pipe  avoided. 

If  the  sewer  is  found  to  be  broken  in  any  place  there  is 
generally  but  one  thing  to  do,  to  dig  down  to  and  replace  it. 
A  sewer  which  is  only  cracked  or  is  leaking  badly  has  been 
repaired  by  inserting  inside  of  it  a  line  of  screw-joint  pipe  as 
large  as  can  be  slipped  into  it,  and  sealing  the  space  between 
the  two  at  the  ends  with  cement.  The  substitution  of  new 
pipe  would  probably  be  cheaper  in  most  cases,  however. 

When  small  pipe  is  only  coated  or  contains  but  little 
deposit  it  is  sometimes  cleaned  by  the  use  of  a  wire  brush,  just 
the  size  of  the  sewer,  fixed  upon  the  end  of  a  rod  similar  to 
those  already  described.  Small  sticks,  jute,  etc.,  can  be  cut  by 
tree-pruning  shears.  Cloth  or  similar  matter  can  be  withdrawn 
by  a  contrivance  like  a  large  corkscrew  on  the  end  of  the  rod. 

The  cleaning  of  sewers  large  enough  to  permit  a  man  to 
work  in  them  needs  no  special  discussion.  If  they  are  large 
enough  the  dirt  may  be  carried  to  the  manhole  in  a  low  car 
running  on  the  sewer  bottom.  In  smaller  sewers  it  may  be 
shovelled  or  hoed  into  a  pile  at  each  of  two  manholes  from  a 
point  midway  between  them  and  removed  in  buckets. 

An  inverted  siphon  may  be  cleaned  as  an  ordinary  sewer, 
after  the  sewage  flow  has  been  diverted  to  the  other  siphon- 
pipe  or  dammed  up  and  the  sewage  contained  in  it  pumped 
out. 


PART   IV. 

SEWAGE  DISPOSAL. 


CHAPTER    XV. 

/ 

DISPOSAL    BY    DILUTION. 

•ART.  81.    u DISPOSAL"  AND  " SEWAGE"  DEFINED. 

The  word  disposal  is  often  "used  where  treatment  would 
be  more  properly  employed.  As  a  matter  of  fact  all  sewage, 
dry  or  water-carried,  must  be  disposed  of  in  some  way  after 
having  been  collected  by  a  sewerage  system.  But  if  this  dis- 
posal consists  of  anything  other  than  throwing  away  the 
sewage  this  may  be  properly  called  a  treatment  thereof. 
These  words  will  be  thus  used  in  this  work — disposal  as  a 
general  term,  treatment  as  a  more  specific  one. 

For  a  proper  consideration  of  the  various  methods  of  dis- 
posal it  will  be  necessary  to  understand  the  results  aimed  at 
and  the  princ  pies  involved.  And  first  we  must  understand 
what  is  implied  by  the  word  sewage.  In  the  dry  sewage  and 
pneumatic  systems  it  means  human  excreta  and  nothing  else. 
In  the  water-carriage  system,  however,  sewage  may  be  found 
to  contain  almost  every  description  of  waste  matter:  faeces, 
house-4 '  slops,"  manufacturing  waste- waters  and  acids,  drain- 
age of  stables,  piggeries,  and  slaughter-houses,  waste  paper  and 
rags,  and  frequently  "  swill,"  and  numberless  matters  which 
should  never  reach  the  sewer.  This  is  ordinarily  called  house- 
sewage.  Into  combined  and  storm  sewers,  besides  rain- 
water, not  only  horse-droppings  and  vegetable  refuse  but 
sand,  clay,  gravel,  and  other  heavy  matters  find  admission 
through  the  street-inlets.  These  go  to  make  what  is  called 
storm-sewage.  The  common  impression  is  that  of  these  the 
human  excrements  alone  are  dangerous;  and  this  is  to  a  large 

359 


360  SEWERAGE. 

extent  true  so  far  as  concerns  dissemination  of  the  germs  of 
disease.  But  it  is  known  that,  aside  from  this,  kitchen-wastes 
are  fully  as  objectionable,  since  they  contain  practically  the 
same  putrescible  matter,  and  in  a  state  less  easily  rendered 
innocuous  by  either  natural  or  artificial  means.  Where  storm- 
water  is  admitted  to  the  sewers  the  large  quantities  of  horse- 
droppings  which  are  washed  in  during  the  first  few  minutes 
of  each  rainstorm  render  the  water  nearly  as  offensive,  if  not 
so  dangerous,  as  do  human  excreta. 

Owing  to  diversity  of  manufacturing  industries,  to  differ- 
ences in  the  characters  of  the  water  used  by  different  towns, 
and  to  other  local  peculiarities  the  sewage  of  each  town  varies 
from  that  of  almost  every  other.  Therefore  the  question  of 
the  proper  disposal  of  this  compound  is  seen  to  be  a  problem 
of  no  easy  solution.  The  difficulty  of  treatment  is  increased 
by  the  exceeding  dilution  of  the  sewage,  since  the  sewage  of 
an  average  American  town  will  contain  less  than  i  part  in  1000 
cf  organic  matter,  i  part  of  mineral  matter,  and  998  to  999 
parts  of  water. 

Difficulty  of  disposal  is  frequently  considered  to  be  con^ 
nected  with  house-sewage  only.  But  if  the  separate  system 
be  used  it  is  generally  desirable  to  connect  with  the  house- 
sewers,  cab-stands,  market-places,  and  other  parts  of  streets 
liable  to  collect  considerable  filth,  small  inlets  being  used  so 
that  only  a  small  amount  of  water  from  any  storm  can  enter 
them,  or  else  special  traps,  ordinarily  closed,  but  through 
which  the  filth  can  be  washed  by  hose. 

ART.  82.     AIMS  OF  DISPOSAL. 

The  first  aim  is  the  getting  rid  of  the  sewage ;  the  dispos- 
ing of  it  in  such  a  way  and  such  a  place  that  it  will  not  create 
a  nuisance.  Communities,  being  even  more  selfish  than  indi' 


DISPOSAL    BY    DILUTION.  361 

viduals,  seldom  regard  the  well-being  of  other  communities, 
but  are  satisfied  if  no  nuisance  is  created  within  their  own 
limits.  It  is  here  that  the  State,  by  its  laws  and  through  its 
Board  of  Health,  should  interfere  for  the  protection  of  each, 
community  against  all  others.  In  England  this  protection  is 
afforded  by  national  laws  and  a  national  board.  In  this  country 
a  number  of  States  within  the  past  few  years  have  enacted  laws 
affording  a  certain  amount  of  such  protection.  The  first  of 
these  was  Massachusetts,  but  Pennsylvania,  New  Jersey,  New 
York  and  Ohio  now  have  excellent  laws  and  many  other  States 
are  falling  into  line.  It  is  a  duty  which  the  engineer  owes  to 
humanity  to  educate  the  people  to  the  importance  of  this  matter; 
though  he  will  often  be  compelled  to  yield,  in  part  at  least,  to  the 
selfish  demands  of  those  for  whom  he  acts,  that  they  be  put  to 
no  expense  for  protection  of  other  communities  not  required  by 
State  or  national  laws. 

Where  this  protection  is  afforded  through  adequate  laws 
properly  enforced  the  disposal  of  the  sewage  must  be  such 
that  it  will  "  lose  permanently  its  power  for  evil."  How 
this  can  best  and  most  economically  be  done  is  the  question 
to  be  solved. 

Many  attempts  have  been  made  at  a  solution  of  this  ques- 
tion of  disposal  which  shall  not  only  meet  the  sanitary 
requirements,  but  which  shall  also  be  financially  remunerative. 
Some  reports  of  success  have  been  heard  of,  but  when  investi- 
gated the  details  are  found  to  be  disappointing.  An  English 
company  which  used  a  method  of  Chemical  Precipitation  was 
reported  as  paying  dividends,  but  inquiry  showed  that  these 
were  but  a  part  of  the  sum  paid  to  the  company  by  the  dis- 
trict for  disposing  of  its  sewage,  and  the  taxpayers  were  but 
little  benefited  in  pocket  by  the  method  employed.  Investi- 
gations of  other  cases  have  resulted  somewhat  similarly.  The 
author  knows  of  no  case  where  the  disposal  of  sewage  is 
accomplished  at  a  profit  to  the  city  or  town.  In  the  case  of 


32  SEWERAGE. 

water-carried  sewage  this  is  not  to  be  wondered  at,  since  the 
value  of  the  manure  contained  in  one  ton  of  Boston's  sewage, 
for  instance,  is  estimated  to  be  but  one  cent. 

The  sewage  of  several  of  our  Western  cities  situated  in  the 
"  desert "  region  is  disposed  of  for  irrigation  at  a  considerable 
profit.  Los  Angeles,  Cal.,  in  1895  received  a  net  revenue  there- 
from, above  all  salaries  and  repairs,  of  $1,140.00,  in  1896  of 
$943.30  and  in  1900  of  about  $3,500.  It  is  reported  that  all  the 
sewage,  however,  is  now  discharged  into  the  Pacific.  Pasadena, 
Cal.,  in  1909  raised  $2,563  worth  of  hay,  $6.601  worth  of  walnuts 
on  no  acres,  and  received  $2,508  from  other  products,  or  a  total 
of  $11,672;  the  cost  of  maintenance  being  $8,517.  The  total 
cost  of  the  farm  (516  acres)  and  implements  has  been  $105,500. 
It  is  proposed  to  plant  oranges  on  55.6  acres  which  were  purchased 
in  1909.  In  general  few,  if  any,  farms  in  districts  where 
irrigation  is  not  necessary,  and  on  which  sewage  must  be 
turned  in  rainy  as  well  as  in  dry  weather,  will  bring  any  con- 
siderable rental;  and  no  other  system  of  treatment  is  known 
which  will  return  any  net  profit  above  running  expenses. 
This  being  the  case,  the  endeavor  should  be  to  find  for  each 
place  that  method  of  disposal  which,  under  the  existing  con- 
ditions of  location,  character  of  sewage,  etc.,  will  best  meet 
the  requirements  both  of  the  State  laws  and  of  the  laws  of 
sanitary  science,  and  which  will  be  least  expensive,  both  first 
cost  and  maintenance  being  considered,  y  w 

ART.  83.     PRINCIPLES  INVOLVED. 

7  For  an  exposition  of  the  principles  involved  we  must  call 
upon  chemistry,  biology,  bacteriology,  medicine,  and  kindred 
sciences.  Their  teachings,  stated  generally,  are: 

That  matter  in  a  state  of  putrescence  is  harmful  to  human 
life  if  taken  into  the  system. 


DISPOSAL    BY    DILUTION.  363 

That  volatile  emanations  from  such  matter  when  breathed 
into  the  lungs  lower  the  tone  of  the  constitution  and  render 
it  more  susceptible  to,  if  they  do  not  indeed  directly  occasion, 
disease. 

That  many  diseases  may  be  contracted  by  taking  into  the 
stomach  certain  germs  which  are  found  to  be  excreted  by 
those  already  sick  of  such  a  disease,  and  these  germs  will 
exist  for  days  in  sewage  having  any  amount  of  dilution. 

That  ordinarily  excreta  do  not  putresce  until  from 
twenty-four  to  sixty  hours  after  its  discharge,  or  even  longer 
under  certain  circumstances,  such  as  absence  of  moisture. 

That  the  only  true  destruction  of  the  dangerous  character- 
istics of  sewage  is  that  effected  by  oxidation  and  by  removal 
of  the  disease-germs. 

That  oxidation  does  not  destroy  but  merely  transforms 
the  putrescible  organic  matter  into  harmless  mineral  com- 
pounds. 

The  legal  principles  involved  vary  in  different  localities 
and  with  different  interpreters  of  the  law,  frequently  depend- 
ing upon  the  ruling  as  to  what  creates  a  nuisance.  "  I  should 
include  under  this  head  any  matter,  whether  solid,  liquid,  or 
gaseous,  which  is  itself  injurious  to  health  or  which  may 
become  so  in  contact  with  other  substances,  whether  the 
latter  may  be  in  themselves  hurtful  or  not;  further,  any 
matter  which,  though  not  demonstrably  poisonous,  is  offen- 
sive to  the  senses."  (Slater,  "  Sewage  Treatment,  Purifica- 
tion, and  Utilization.")  Such  disposition  of  any  matter  that 
it  may,  while  in  the  condition  above  described,  approach 
within  effective  distance  of  any  dwelling  or  occupied  land 
should  be  held  to  be  a  nuisance.  A  recent  ruling  in  fhe 
United  States  has  included  in  the  "  creating  of  a  nuisance  " 
the  rendering  unfit  for  drinking  purposes  water  which  would 
otherwise  be  used  thus.  Under  properly  prepared  State  laws, 
interference  with  the  health  and  rights  of  others  should  be 


364  SEWERAGE. 

preventable  by  injunction,  or,  in  the  case  of  injury  to  manu- 
facturing interests,  should  subject  the  city  to  forfeiture  of 
damages.  An  interesting  case  under  the  latter  head  is  that 
decided  in  1898  against  New  York  City,  and  in  favor  of  an 
oysterman  whose  beds  were  destroyed  by  the  discharge  from 
a  near-by  sewer  outlet,  and  who  was  awarded  their  value  in 
damages.  (See  Engineering  Record,  vol.  XXXVIII.  page  I.) 
In  1900  the  New  York  Supreme  Court  decided  that  an  injunc- 
tion could  be  obtained  restraining  a  city  from  so  polluting  a 
stream  as  to  injure  land  or  stock,  but  that  damages  could  not 
be  collected  from  a  municipal  jcorporation,  although  they 
could  be  from  a  private  one.  TrS^preme  Court  of  Connec- 
ticut has  held  that:  "  The  discharge  of  sewage  and  other  noxious 
matters  into  an  inland  stream  to  the  injury  of  a  riparian  pro- 
prietor below  has  been  held  to  be  an  unlawful  invasion  of  the 
rights  of  said  proprietor,  remediable  by  injunction,  by  the  courts 
of  nearly  every  State,  by  the  federal  courts,  and  by  the  courts 
of  England."  (Morgan  et  al.  vs.  City  of  Danbury,  Conn.)  In 
1898  the  California  Superior  Court  granted  an  injunction  against 
the  city  of  Santa  Rosa  from  emptying  into  a  creek  impure 
effluent  from  sewage  irrigation.  The  Indiana  Supreme  Court, 
in  1900,  decided  that  a  municipality  could  not  be  enjoined  from 
discharging  sewage  into  any  stream.  In  the  same  year  the 
Virginia  Supreme  Court  decided  that  neither  municipal  nor 
private  corporations  can  pollute  a  stream  by  sewage  or  otherwise 
without  being  liable  for  damages  for  any  injury  caused. 

From  a  sanitary  and  engineering,  rather  than  a  legal  stand- 
point, it  is  a  mooted  question,  concerning  which  sanitarians  as 
well  as  city  officials  and  legal  experts  disagree,  as  to  how  much 
purification  it  is  proper  to  require  of  cities  and  of  private  indi- 
viduals who  discharge  sewage  and  other  polluted  water  into  streams. 
It  is  possible  for  sewage  to  be  transformed  into  clear  and  prac- 
tically harmless  drinking  water,  but  this  would  be  very  expensive 
in  the  majority  of  cases.  At  very  much  less  expense  sewage  can 


DISPOSAL    BY    DILUTION.  365 

be  so  freed  of  organic  matters  that  there  will  be  little  or  no  danger 
of  its  creating  a  nuisance  after  being  discharged  into  a  stream 
on  tidal  water;  the  amount  of  purification  required  depending 
to  a  considerable  degree  upon  the  amount  and  character  of  the 
water  which  receives  the  effluent.  It  is  also  possible  to  almost 
entirely  sterilize  a  sewage  effluent  without  removing  more  than 
the  grosser  impurities.  In  the  great  majority  of  cases  the  effluent 
should  be  such  as  will,  after  discharge  into  the  stream  which 
ceives  it,  create  no  nuisance;  where  it  is  discharged  in  to  a  large 
body  of  salt  water  where  tides  and  currents  will  remove  it  from 
the  neighborhood  of  the  land,  it  may  be  that  no  purification 
whatever  will  be  needed.  (But  in  this  case  the  possibility  of 
shoaling  of  channels  by  deposits  should  be  borne  in  mind). 
Where  there  are  shellfish  reached  by  the  effluent  it  is  generally 
considered  that  practical  sterilization  is  desirable. 

In  the  case  of  fresh-water  streams,  however,  even  those  which 
may  be  drawn  upon  for  water  supplies  lower  down,  there  is 
considerable  difference  of  opinion.  Some  maintain  that  effluents 
reaching  these  should  be  freed  from  all  putrescible  organic  matter 
and  also  be  practically  sterile.  Others,  however,  claim  that 
cities  or  private  companies  desiring  to  use  the  water  for  drinking 
supplies  can  make  such  supplies  safe  only  by  purification,  even 
though  it  receive  no  sewage,  since  other  sources  of  pollution  remain 
which  it  is  almost  impracticable  to  eliminate;  and  that,  this  being 
the  case,  it  would  cost  little  if  any  more  to  effect  the  purification 
if  the  stream  received  sewage  effluents  more  or  less  high  in  sewage 
bacteria.  Moreover,  the  cost  of  removing  the  bacteria  from 
comparatively  clear  river  water  is  much  less  than  that  of  removing 
them  from  sewage  or  even  from  an  effluent  previous  to  dilution 
in  the  river;  and  that  therefore  the  minimum  cost  to  both  com- 
munities considered  together  would  result  from  the  sewage  filter 
removing  organic  matter  only  and  the  water  filter  removing  the 
bacteria. 

It  is  seen  that,  whichever  of  the  above  arguments  be  accepted, 


366  SEWERAGE. 

some  purification  must  be  given  to  sewage  which  is  discharged 
into  a  fresh-water  stream,  unless  this  be  of  great  volume  of  flow; 
the  difference  being  in  the  degree  of  purification  demanded. 

In  a  few  States  sewerage  systems  must  be  so  designed, 
before  meeting  the  approval  of  the  State  Boards  of  Health 
(which  is  by  law  made  a  necessary  prerequisite  to  construction), 
as  to  permit  and  provide  for  a  treatment  of  the  house  sewage 
at  some  future  time,  even  if  they  are  allowed  temporarily  to 
discharge  into  adjacent  streams.  It  is  probable  that  before 
very  many  years  this  will  be  the  regulation  in  most  States. 
But,  in  any  event,  where  the  discharge  is  into  a  stream  or  lake 
the  possibility  of  the  necessity  arising  in  the  future  for  treat- 
ment of  the  sewage  should  be  foreseen  and  provided  for  in 
the  design  of  the  system.  It  is  advisable  both  to  consult  the 
State^  Board  of  Health  and  to  obtain  reliable  legal  advice 
before  deciding  finally  the  question  of  disposal. 

FOLLOWING  is  a  list  of  references  to  the  statutes  of  twenty- 
two  States  referring  to  the  POLLUTION  OF  WATER  : 
California.      Criminal  Code  (1886),  Sees.   1357,  1376. 
Connecticut.      General  Statutes  (1888),  Sees.  2652-5.      Chap- 
ters 28  and  203  of  1895. 
Delaware.      Revised  Code  (1893),   p.  926.      Delaware  Laws, 

Vol.  XII,  Chapter  405. 
Illinois.     Annotated  Statutes  (1896),   Chapter  38,  Sees.  369 

(2),  (3);  Chapter  24,  Art.   10,  Sec.  2. 
Indiana.      Statutes  (1897),  Sees.  2017,  2195. 
Jowa.      Code  (1897),  Sec.  4979- 

Kansas.      General  Statutes  (1897),  Chapter  IOO,  Sees.  338-9, 
Kentucky.     Statutes  (1894),  Sec.  1278. 
Maine.     Chapter  82  of  1891. 

Maryland.     Public  General  Laws  (1888),  Vol.  I,  p.  550,  Sec. 
277. 


DISPOSAL    BY    DILUTION.  367 

Massachusetts.     Public    Statutes    (1882),    Chapfer    80,    Sees. 

96-7,  101-2.      Chapter  208,  Sees.  7-8.      Chapter  172  of 

1884.      Chapter  274  of  1886.      Chapters   1 60  and  375  of 

1888. 

Michigan.     Compiled  Laws  (1897),  Sec.  11,432. 
Minnesota.     Statutes  (1894),  Sees.  430-1,  6642.     Laws  of  1905, 

Chapter  236,  Sees.  5  and  20. 
New  Hampshire.      Public  Statutes  (1891),  Chapter  108,  Sees. 

13-15.      Act  of  March  28,  1895. 
New  Jersey.     General  Statutes  (1895),  p.  1644,  Sec.  49;  (XJI) 

pp.   1107,   1109,  2215. 

New  York.      Revised  Statutes  (1895),  p.  2437,  Sees.  70-72^. 
North  Carolina.     Act  of  March  i,  1893,  18-21. 
Ohio.     Annotated    Statutes   (1900),    Sees.    409,    (26),   6921, 

6923,  6925. 

Oregon.     Annotated  Laws  (1892),  Sec.  198. 
Tennessee.      Code  (1896),  Sec.  6869. 

Virginia.      Code  (1887),  Sec.  3812.      Chapter  460  of  1892. 
West  Virginia.      Code  (1899),  Chapter  150,  Sec.  2Q>b  and  c. 

ART.  84.     COMPOSITION  OF  SEWAGE. 

Being  composed  of  house-wastes  and  wastes  from  manu- 
facturing processes  carried  in  suspension  and  solution  by 
water,  sewage  is  found  to  contain  all  the  matters  contained 
in  these,  either  in  their  original  forms,  or  combined  accord- 
ing to  their  affinities  into  new  compounds,  or  partly  decom- 
posed into  their  elements.  In  either  the  combination  or 
decomposition  gases  may  be  formed,  and  in  these  and  in 
vapors  a  small  percentage  of  certain  elements  in  the  sewage 
may  escape  to  form  the  "  sewer  air." 

Of  the  various  constituents  of  sewage,  a  large  proportion 
are. harmless;  some,  while  in  themselves  harmless,  may  form 
compounds  which  are  noxious,  or  may  interfere  with  the 


368 


SEWERAGE. 


purification;  others — the  organic  matters — are  offensive  and 
dangerous  to  animal  life  while  undergoing  decomposition,  in 
which  state  they  are  always  found  in  sewage;  and  of  the 
bacteria  many  are  harmless,  but  an  indefinite  number  are 
fatal  to  human  life.  Purely  mineral  elements  and  compounds 
are  seldom  found  in  sewage  in  such  quantities  as  to  be 
injurious  if  taken  into  the  stomach. 

Table  No.  25  shows  the  weight  in  pounds  per  day  of  the 
solid  and  liquid  excrements  of  a  mixed  population  of  100,000* 
and  also  the  same  divided  by  the  weight  of  100  gallons  (the 
assumed  per  capita  water  consumption),  giving  the  parts  by 
weight  per  100,000  which  the  excrements  would  contribute 
to  the  sewage.  If  the  consumption  is  not  100  gallons, 
multiply  by  100  and 'divide  by  the  consumption. 

TABLE  No.  25A. 

AMOUNT    OF    EXCREMENTAL    ORGANIC    MATTER    IN    SEWAGE. 
(From  Wolff  &  Lehmann.) 


Faeces. 

Urine. 

Total. 

c 

V 

c 

a 

c 
o 

« 

.0  &e 

rt 
a 

.y  o* 

3 

ll 

3 

^4 

C       +* 

a 

* 

a 

^j 

a 

ft 

J*z 

o 

rt 
o 

fe 

0 

Sz 

§ 

H 

0 

£ 

H 

0 

£ 

H 

0 

IV 

Pounds  per  day  

20,000 

294 

4*3 

257,920 

2311 

1037 

277,920 

2605 

1450 

Parts  per  100,000    parts  of 

sewage   (water  consump- 

tion  100  gallons  per  day) 

24.09 

0.35 

0.50 

3°9-S 

2.77 

1.24 

333.60 

3.12 

1-74 

TABLE  No.  25s. 

POUNDS   OF   ORGANIC    MATTER    PER    CAPITA    PER    DAY. 
Average  of  Several  Massachusetts  Plants. 


Residue  on  Evaporation. 

Ammonia. 

Chlo- 
rine. 

Total 

Nitrogen. 

Bacteria, 
Billions 
.per  capita 
per  day. 

Loss  on  Ignition.    1              Fixed. 

Dis- 
solved. 

Sus- 
pended. 

Dis- 
solved. 

Sus- 
pended. 

Free. 

Albumin- 
oid. 

•  0594 

.0836 

.  1276 

.0242 

.0110 

.0031 

•0352 

.0213 

300 

DISPOSAL    BY    DILUTION.  369 

These  matters  will  constitute  most  of  the  pollution  found  in  the 
sewage,  excepting  such  as  may  come  from  tanneries,  breweries, 
slaughter-houses,  and  markets.  The  principal  constituents 
of  organic  matter  are  carbon,  oxygen,  nitrogen,  and  hydrogen. 
All  contain  carbon,  but  all  do  not  contain  nitrogen.  Those 
containing  nitrogen  are  in  general  the  more  liable  to  putrefy, 
and  are  regarded  as  the  more  objectionable.  For  this  reason 
the  quantity  of  nitrogen  and  its  compounds  in  sewage  is  that 
most  carefully  determined  as  an  indication  of  the  quantity  of 
harmful  organic  matter  present. 

The  pollution  from  manufacturing  establishments  may 
consist  of  almost  any  acids,  alkalis,  or  organic  matters.  A 
carpet,  blanket,  and  cloth  mill  on  the  Schuylkill  used  daily, 
a  few  years  ago,  48,700  pounds  of  organic  matter,  including 
1 8  different  substances,  2520  pounds  of  21  different  acids, 
and  950  pounds  of  6  different  alkalis  Brass-works  discharge 
considerable  sulphate  of  copper,  cyanide  of  potash,  and  oils; 
the  chief  waste  from  iron-works  is  sulphate  of  iron;  from 
paper-mills  come  filaments  of  jute,  cotton,  and  other  organic 
matters,  caustic  soda,  chloride  of  lime,  and  sulphite;  in 
woollen-factories  the  washing  of  the  wool  produces  large 
amounts  of  organic  wastes,  and  there  are  also  discharged  soda 
alkalis,  logwood,  fustic,  madder,  copperas,  potash,  alum, 
blue  vitriol,  muriate  of  tin,  and  other  dye-wastes;  from 
cotton-factories  come  sulphuric,  nitric,  and  muriatic  acids, 
chloride  of  lime,  soda,  potash,  alum,  copperas,  blue  vitriol, 
lime,  pearl-ash,  stannate  of  soda,  sugar  of  lead,  indigo, 
cutch,  sumac,  alkali,  soda,  and  various  aniline  dyes;  from 
silk-factories,  sericine,  or  silk  gum,  soda,  and  a  small  amount 
of  dyestuffs.  Many  of  the  acids  and  alkalis  from  factories 
neutralize  each  other,  and  the  principal  objection  to  these  in 
sewage  is  that  they  may  form  insoluble  compounds  or  foul 
gases,  or  that  the  acidity  of  the  sewage  may  interfere  with 
the  later  treatment.  In  some  instances  acids  discharged 


37°  SEWERAGE. 

from  brass-work  and  iron-mills  are  sufficient  in  quantity  to 
kill  the  fish  in  a  river,  and  of  course  to  render  it  unfit  for 
drinking-water.  An  occasional  advantage  experienced  from 
acid  sewage  is  the  destruction  of  considerable  percentages  of  the 
contained  bacteria. 

The  water  itself  before  pollution  generally  contains  little 
organic  but  some  mineral  matter.  Lime,  chlorine,  and  iron 
are  the  minerals  most  commonly  found  in  solution.  Sand 
and  clay  are  generally  found  in  suspension  in  varying  quanti- 
ties. Copper,  zinc,  lead,  and  other  metals  are  sometimes 
found  in  small  quantities.  Lime  causes  the  "  hardness"  of 
water,  which  is  classified  as  either  "permanent  "  or  "  tempo- 
rary." The  former  is  caused  by  calcium  sulphate  and  other 
soluble  salts  of  calcium  and  magnesium,  not  carbonates,  held 
in  solution;  such  water  cannot  be  materially  softened  by 
boiling.  Temporary  hardness  is  due  to  carbonates  of  calcium 
and  magnesium ;  by  boiling  such  water  the  carbonic  acid  is 
expelled  and  the  salts  become  insoluble. 

Chlorine  is  found  in  most  waters,  being  washed  from  the 
soil,  or  from  the  air  where  it  has  been  carried  by  ocean 
vapors.  It  is  unobjectionable  in  the  quantities  ordinarily 
found,  but  is  significant  in  sewage  for  two  reasons:  first,  if 
more  than  normal  in  quantity,  it  is  an  almost  sure  indication 
,of  sewage  contamination,  and  if  not  more  than  normal,  that 
there  has  been  no  sewage  contamination;  second,  it  cannot 
be  removed  from  solution  and  hence  remains  constant  through 
all  filtration  and  other  purification  processes,  thus  serving  as 
an  index  of  the  strength  of  domestic  sewage,  whether  purified 
or  not.  The  amount  of  chlorine  in  a  sample  of  purified 
effluent  and  in  the  sewage  from  which  it  was  derived  must  be 
practically  the  same.*  To  determine  pollution  from  the 

*  For  some  reason  not  understood  the  chlorine  in  effluents  from  puri- 
fication processes  is  generally  a  very  little  lower  than  that  in  the  crude 
sewage. 


THE  SEWAGE-TREATMENT  PROBLEM. 


37* 


PLATE  XII.— ISOCHLORS  OF  MASSACHUSETTS  AND  CONNECTICUT. 


372  SEWERAGE. 

amount  of  chlorine  present  it  is  necessary  to  know  the  normal 
amount  in  the  district  in  question.  This  ordinarily  varies 
with  the  distance  from  the  ocean,  being  least  in  those  locali- 
ties which  the  ocean  winds  must  travel  farthest  to  reach; 
excepting,  of  course,  those  places  where  the  ground-waters 
are  rich  in  salt,  as  in  west-central  New  York.  Plate  XIII 
shows  the  distribution  of  chlorine  in  the  normal  waters  of 
Massachusetts  and  Connecticut.  It  is  seen  to  reach  a  maxi- 
mum of  2.42  parts  per  100,000  on  Cape  Cod. 

Iron  is  to  be  found  in  small  quantities  in  most  waters,  but 
this  and  other  metallic  substances  have  no  significance  in 
sewage  except  as  they  may  affect  purification. 

The  organic  and  mineral  matter  in  suspension  and  solution 
in  the  water  before  the  addition  of  sewage  matters  will  of 
course  be  included  in  that  found  in  the  resultant  sewage,  and 
it  is  desirable  to  learn  what  this  amount  is.  The  Naugatuck 
River  at  Union  City,  Conn.,  contained,  as  extremes,  in  Sept. 
1897,  6.05  parts  per  100,000  of  mineral  and  2.20  of  organic 
matter,  2.00  parts  being  lime  and  .42  chlorine;  and  in  April 
1896,  but  1. 60  of  mineral  and  1.55  of  organic  matter;  these 
being  fairly  average  results  for  New  England  in  a  thickly 
populated  district. 

The  above  illustrates  in  a  general  way  the  .constitution  of 
sewage ;  but  to  understand  the  methods  and  processes  which 
sewage  undergoes  during  purification  it  is  necessary  to  study 
the  chemical  conditions  and  forms  in  which  these  matters 
exist  in  sewage,  as  well  as  those  in  which  they  generally 
appear  in  chemical  analyses.  Average  American  sewage  con- 
tains about  40  to  70  parts  per  100,000  of  solids  when  the  water 
consumption  is  60  to  80  gallons  per  capita.  Of  these  about  15 
to  30  will  be  in  suspension  and  the  remainder  in  solution.  The 
•  older  the  sewage  and  the  more  it  has  been  agitated  the  greater 
Iwill  be  the  proportion  of  solid  matter  in  solution.  Of  those  in 
suspension  3  to  10  parts  are  mineral  and  12  to  20  are  organic; 


DISPOSAL   BY    DILUTION.  373 

of  those  in  solution  20  or  30  are  mineral,  5  to  10  are  organic. 
Owing  to  causes  already  mentioned,  as  well  as  to  the  great  varia- 
tions in  per  capita  water  consumption  in  different  places,  any 
individual  sewage  may  vary  greatly  from  the  above  figures;  but 
they  serve  to  give  a  general  idea  of  the  relative  proportions.  The 
average  amounts  of  these  constituents  per  capita  in  a  number  of 
American  cities  is  given  in  Table  No.  26. 

The  above  figures  are  from  New  England  cities,  and  are 
approximately  the  same  as  those  found  in  average  English  sewages. 

cities  where  the  water  consumption  is  much  greater  the  sewage 
will  be  proportionately  weaker.  In  comparatively  strong  sewage 
the  amount  of  solid  and  organic  matter  is  fully  twice  as  great  in 
the  day  flow  as  in  the  night  flow;  and  in  weaker  sewages,  the 
difference  may  be  still  greater. 

The  proportions  of  the  various  constituents  are  stated  by 
some  chemists  in  parts  per  hundred  thousand;  by  others  in 
parts  per  million,  or,  which  is  practically  the  same  thing,  in 
milligrams  per  liter;  others  in  grains  per  U.  S.  gallon;  and 
by  many  English  chemists  in  grains  per  Imperial  gallon.  The 
last  can  be  reduced  to  parts  per  100,000  by  dividing  by  7  and 
multiplying  by  10;  grains  per  U.  S.  gallon  by  dividing  by  5.8335 
and  multiplying  by  10.  In  this  work  parts  per  100,000  will 
foe  used  unless  otherwise  stated. 

About  40  ounces  per  day  of  human  urine  is  excreted  per 
capita,  on  an  average,  and  3  ounces  of  wet  faeces  (see  page 
368).  Of  the  urine  about  0.337  grain  is  common  salt,  0.2 
being  chlorine.  In  the  excrements  occurs  the  great  bulk  of 
the  nitrogen  found  in  sewage,  mostly  as  albuminous  com- 
pounds. This  leaves  the  body  in  the  form  of  urea,  of  which 

the  composition  is  CO  j  Njj2-       It    is    quickly    attacked    by 


either  the  bacillus  ureae  or  micrococcus  ureae,  or  both.  Each 
of  these,  breaking  down  the  urea,  convert  it  into  carbonate  of 
ammonia  thus  : 


374  SEWERAGE. 

Urea.  Water.        Carbonate  of  ammonia* 

C0  {  NH*.  +  2(H'0)  =  (NH.)'CO>- 

"  If  the  sewage  is  kept  without  undergoing  purification 
for  a  day  or  so,  it  undergoes  putrefaction  and  begins  to  give 
off  foul  emanations;  in  the  course  of  two  or  three  days  the 
albuminous  matters  begin  to  split  up,  and  the  sewage,  p..r- 
ticularly  when  the  water  contains  sulphates,  yields  sulphu- 
retted hydrogen,  which  is  known  by  its  characteristic  odor  of 
rotten  eggs.  When  this  gas  is  formed  the  sewage  becomes 
black.  As  the  above  changes  take  place,  more  and  more  of 
the  solid  matter  enters  into  solution."  (Barwise,  "Purification 
of  Sewage.") 

Vegetable  refuse  occasions  much  of  the  foulness  of  stale 
sewage,  largely  because  of  the  sulphur  it  contains.  Putrefac- 
tion is  preceded  by  the  combination  of  part  of  the  nitrogen 
and  carbon  with  all  the  free  oxygen  and  with  part  of  that 
contained  in  the  nitrates. 

It  is  evident  that  the  form  under  which  the  nitrogen  is 
found  will  depend  to  a  considerable  degree  upon  the  amount 
of  decomposition  which  the  organic  matter  has  undergone. 
This  decomposition  is  facilitated  by  comminution  of  the 
particles  in  suspension,  such  as  occurs  in  pumping,  and 
increases  with  time,  and  its  character  is  determined  by  the 
amount  of  oxygen  contained  in  the  sewage  water.  In  a  short 
time  after  entering  the  sewers  sewage  ordinarily  contains  no 
dissolved  oxygen  and  no  nitrogen  in  the  form  of  nitrates; 
although  when  fresh  it  contains  some  free  oxygen  and  gener- 
ally nitrates  and  nitrites. 

Sewage  contains  countless  numbers  of  bacteria  of  many 
varieties,  as  many  as  30,000,000  in  a  cubic  centimeter  having 
been  estimated,  of  200  or  more  varieties.  One  of  the  most 
important  is  the  Bacillus  coli  communis,  which  originates  in 
the  animal  intestine.  Most  of  these  bacteria  are  harmless; 


DISPOSAL    BY    DILUTION.  375 

many  are  beneficial  in  breaking  down  complex  organic  com- 
pounds and  assisting  in  the  oxidation  of  the  sewage ;  but  a 
few  are  the  cause  of  disease  if  taken  into  the  human  system. 
Among  the  last  are  the  bacterium  of  cholera  (Spirillum 
cholerae  asiaticae)  and  that  of  typhoid  fever  (Bacillus  typhosus). 
B.  coli  communis  and  B.  enteritidis  sporogenes  are  the  bac- 
teria most  easily  identified  as  directly  derived  from  excrement. 
The  former  is  most  abundant  in  sewage-polluted  water;  the 
latter  is  not  so  abundant,  but  is  much  more  probably  patho- 
genic, being  a  possible  cause  of  acute  diarrhoea.  There  are 
also  present  in  sewage  large  numbers  of  enzymes,  lifeless 
organic  substances  which  exert  chemical  action  in  breaking 
down  complicated  organic  molecules.  Such  are  pepsin,  pan- 
creatin,  and  other  digestive  ferments.  Their  mode  of  action 
is  not  well  understood,  v/ 

ART.  85.     SEWAGE  ANALYSES. 

If  sewage  be  heated  in  a  platinum  dish  until  evaporated, 
a  solid  residue  is  left,  composed  of  mineral  and  organic 
matter.  If  this  be  weighed  and  then  heated  to  a  low  red 
heat,  the  organic  matter  will  be  almost  entirely  burned  up, 
while  the  mineral  will  be  but  little  if  at  all  changed.  The 
difference  in  weight  before  and  after  burning  will  be  almost 
exactly  the  amount  of  organic  matter  in  the  sewage.  The 
first  amount  is  generally  called  "residue  on  evaporation  "  or 
"total  solids";  the  burned  part,  "  loss  ,on  ignition"  or 
"  organic  residue"  and  the  unburned  part  the  "  fixed  resi- 
due "  or  ''mineral  residue."  If  a  sample  of  the  raw  sewage 
be  filtered  through  fine  filter-paper,  that  in  suspension  will 
be  intercepted,  and  the  difference  between  this  and  the  total 
amount  of  solids  will  give  the  amount  in  solution.  If  each  of 
these  be  heated  so  as  to  burn  the  organic  matter,  the  amount 
of  this  in  suspension  and  that  in  solution  are  ascertained. 


376  SEWERAGE. 

Organic  matter,  as  it  decays,  gives  off  carbonic  acid, 
which  in  part  remains  in  solution  and  in  part  escapes.  The 
ammonia  resulting  from  the  decay  is  taken  into  solution. 
Other  organic  matter,  about  ready  to  decay,  gives  up 
ammonia  when  the  sewage  is  boiled.  The  ammonia  in  solu- 
tion, and  the  ammonia  thus  set  free  from  the  organic  matter 
in  the  sewage,  pass  off  in  the  steam  in  a  short  boiling;  and 
if  this  steam  be  again  condensed,  the  ammonia  is  all  held  in 
solution  and  its  quantity  can  be  readily  determined.  This  is 
the  quantity  of  ammonia  called  "  free  ammonia,"  and,  being 
the  product  of  decay,  is  the  most  characteristic  ingredient  of 
stale  sewage.  "  Free  ammonia"  is  not  chemically  "  free," 
but  is  generally  in  combination  with  carbonic  and  organic 
acids,  or  even  appears  as  chloride  or  sulphate  of  ammonia. 

There  is  still  a  quantity  of  combined  nitrogen  in  the 
remaining  organic  matter,  called  "organic  nitrogen,"  about 
two-sevenths  of  which  can  be  made  to  pass  off  as  ammonia 
by  putting  into  the  sewage  an  alkaline  solution  of  perman- 
ganate of  potash — a  strong  oxidizing  agent — and  again  boil- 
ing, the  ammonia  thus  obtained  being  called  "  albuminoid  " 
or  "organic  ammonia."  Albuminoid  ammonia  is  being 
constantly  changed  by  decomposition  into  free  ammonia,  and 
hence  the  older  the  sewage  is  the  greater  the  proportion  of 
the  latter  to  the  former.  When  comparing  two  samples  of 
sewage  by  their  ammonias  we  must  remember  that  free 
ammonia  is  largely  the  result  of  decomposition  of  that  pre- 
viously, but  not  now,  existing  as  organic  matter 

In  oxidation,  upon  which  sewage  purification  largely 
depends,  nitric  acid  is  formed  from  the  nitrogen  of  the 
ammonia  and  of  the  organic  matter  and  the  oxygen  of  the 
air.  This  strong  acid  immediately  combines  with  the  potash, 
soda,  lime,  or  other  base  in  the  sewage,  forming  nitrates  of 
potash,  soda,  etc.,  which  are  entirely  harmless  in  the  quanti- 
ties found  in  the  strongest  sewage  effluent.  The  nitrogen 


DISPOSAL    BY    DILUTION.  377 

contained  in  these  salts  is  called  ''nitrogen  as  nitrates"  or 
"as  nitrites,"  or  simply  "nitrates"  and  "nitrites";  the 
nitrites  being  nitrous  acid  salts  in  which  the  oxidation  is 
carried  less  far  than  in  the  nitrates  owing  to  lack  of  oxygen. 
(Nitrites  are  also  formed  by  the  combination  of  nitrates  and 
unoxidized  matter,  the  former  sharing  its  oxygen  with  the 
latter.)  This  is  probably  the  most  important  chemical  de- 
termination made  of  sewage.  The  organic  matter  may  vary 
Crom  3  to  100  parts  of  sewage.  It  would  be  unusual  to  find 
as  much  as  .01  part  of  nitrogen  as  nitrates  or  nitrites  in 
sewage;  but  in  the  effluent  or  purified  sewage  as  much  as  5 
or  6  parts  may  be  found.  Some  analysts  determine  the  "total 
nitrogen,"  generally  by  the  Kjeldahl  process.  This  is  a  most 
important  test,  but  one  difficult  to  make. 

If  a  portion  of  sewage,  made  slightly  acid  with  sulphuric 
acid  (if  necessary),  is  digested  with  a  solution  of  permanganate  of 
potash  the  carbon  in  the  organic  matter  will  be  oxidized.  This 
test  gives  an  approximate  idea  of  the  amount  of  carbonaceous 
organic  matter  present,  this  being  expressed  in  terms  of  "oxygen 
consumed." 

The  amounts  of  turbidity  and  sediment  in  effluents  are  some- 
times determined,  because  of  their  relation  to  the  creation  of  a 
nuisance  or  to  unsightliness  in  the  stream. 

Methods  for  making  most  of  the  above  tests  were  recommended 
by  the  American  Public  Health  Association  in  1905  ;  but  improve- 
ments are  constantly  being  made  by  chemists,  either  in  accuracy, 
delicacy  or  facility  of  the  several  methods. 

Recent  developments  have  occasioned  a  demand  for  a  method 
of  determining  putrescibility  of  effluents;  of  discriminating 
clearly  between  putrescible  organic  matter  and  more  stable 
humus-like  compounds  which  do  not  undergo  putrefactive  de- 
composition. Oxygen  consumed  by  permanganate  bears  a 
variable  relation  to  the  organic  matter  which  is  oxidizable  under 
natural  conditions;  and  the  "smell"  test  is  inexact.  The  Man- 
chester "incubator"  test  is  somewhat  more  satisfactory,  but 


378  SEWERAGE. 

yields  abnormal  results  at  times,  and  gives  but  a  rough  classifica- 
tion. This  test  consists  of  determining  the  oxygen  absorbed  by 
a  sample;  then  completely  filling  a  bottle  with  the  same  and  plac- 
ing it  in  an  incubator  at  80°  F.  for  five  days;  after  which  it  is 
again  tested  for  oxygen  absorbed.  Increase  in  this  is  an  indica- 
tion of  putrefaction  during  incubation;  but  if  the  sample  has 
remained  sweet  there  will  be  a  somewhat  less  amount  of  oxygen 
absorbed  after  incubation.  An  effluent  of  diluted  sewage  which 
remains  sweet  after  this  test  is  in  no  danger  of  further  putrefac- 
tion— that  is,  will  not  create  a  nuisance — unless  further  polluted. 
At  present  (1910)  the  test  most  commonly  used  is  the  methylene 
blue  test  devised  by  Spitta  in  1903  and  later  perfected  by  others. 
About  i  cc.  of  a  o.i %  solution  of  the  dye  is  added  to  250  cc.  of  the 
sewage  effluent  in  a  glass-stoppered  bottle,  and  this  is  incubated 
at  either  20°  C.  or  37°  C.  The  blue  color  remains  practically 
unchanged  until  the  available  oxygen  contained  (both  free  and  in 
nitrates  and  nitrites)  has  been  used  up  and  the  condition  become 
putrefactive,  when  decolorization  begins.  The  time  required  for 
this  is  the  measure  of  the  degree  of  putrescibility.  Retention  of  color 
for  four  days  at  20°  C.  or  two  days  at  37°  C.  indicates  good  stability. 

The  fat  content  of  sewage  is  important  as  to  its  effect  on  the 
working  of  treatment  processes;  and  this,  or  more  specifically 
the  ether-soluble  matter,  in  crude  sewage  is  sometimes  determined. 

Table  No.  26  gives  the  analyses  of  the  sewage  of  several  cities. 
As  an  illustration  of  the  chemical  effect  of  purification  by  oxida- 
tion, the  Lawrence  sewage  is  seen  to  lose  by  filtration  89%  of  the 
organic  matter  ("loss  on  ignition").  The  free  and  albuminoid 
ammonia  is  reduced  99.1%,  most  of  that  lost  appearing  as  nitrates 
in  the  effluent.  The  chlorine  is  practically  unchanged,  as  it 
should  be.  The  bacteria  are  reduced  99.97%. 

In  the  Meriden  sewage  is  seen  the  effect  of  dilution  in  the 
decreased  chlorine.  If  the  ground-water  contained  0.2  part 
of  chlorine  and  the  sewage  45.8,  there  would  appear  to  be  in 
the  effluent  analyzed  about  45%  as  much  ground-water  as  true 
sewage  effluent.  The  true  amount  of  purification  would 


THE   SEWAGE-TREATMENT  PROBLEM. 


379 


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380  SEWERAGE. 

therefore  probably  be  shown  if  each  quantitative  determina- 
tion for  the  effluent,  diminished  by  30$  of  the  amount  of  the 
same  substance  found  in  normal  ground-water,  be  multiplied 
by  about  1.45. 

It  appears  from  analyses  5  and  6  that  the  free  ammonia 
in  sewage  increased  during  its  flow  through  the  sewers  at  the 
expense  of  the  albuminoid.  Also  that  the  number  of  bacteria 
was  practically  doubled.  It  is  believed  that  this  increase  in 
this  and  in  all  sewage  is  of  non-pathogenic  bacteria  only, 
since  sewage  appears  to  be  an  unfavorabl~  breeding-place  for 
the  pathogenic  varieties. 

The  result  of  a  bacterial  analysis  is  generally  stated  as  a 
certain  number  of  bacteria  per  cubic  centimeter.  This  num- 
ber frequently  runs  up  into  the  millions,  of  which  it  is  evident 
that  no  direct  count  could  have  been  made.  To  obtain  practi- 
cable  conditions  a  small  amount  of  sewage  is  diluted  with  1000 
to  100,000  times  its  volume  of  sterile  water,  and  the  number 
of  bacteria  found  in  this  mixture  per  cubic  centimeter  is  mul- 
tiplied by  the  proportion  of  dilution.  How  many  of  the 
bacteria  are  pathogenic  it  is  impossible  to  say  with  our  present 
knowledge  of  bacteriology  and  methods  of  analyzing ;  for  the 
rinding  of  the  bacterium  of  typhoid  fever  or  cholera  in  sewage 
is  an  unusual  occurrence,  so  few  are  they  in  comparison  with 
the  total  number  present.  If  there  was  one  such  bacterium 
in  each  cubic  centimeter  of  a  given  sewage,  and  this  was  di- 
luted 10,000  times  for  analysis,  the  chance  of  this  bacterium 
being  present  in  the  analyzed  sample  would  be  but  one  in  ten 
thousand ;  but  if  this  sewage  be  discharged  into  50  times  its 
volume  of  water,  each  glassful  of  this  would  be  likely  to  con- 
tain five  or  six  typhoid  bacilli.  It  is  therefore  apparent  that 
the  absence  of  pathogenic  bacteria  from  an  analyzed  sample 
by  no  means  indicates  that  they  are  not  present  in  the  sewage 
in  great  numbers.  This  is  of  little  importance  in  an  analysis 
of  sewage,  since  it  should  be  assumed  that  the  excreta  of  a 


THE  SEWAGE-TKEATMENT  PROBLEM. 


typhoid  patient  containing  millions  of  these  may  at  any  time 
enter  the  sewer.  It  is  desirable,  however,  to  learn  to  what 
extent  such  bacteria  are  removed  by  purification  or  otherwise, 
and  on  this  point  there  is  still  great  uncertainty.  But  it  is  in 
general  assumed  that  any  reduction  in  the  total  number  of 
bacteria  is  at  least  no  greater  than  that  in  the  number  of 
pathogenic  ones  in  proportion  to  the  number  originally 
present.  It  is  now  thought  that  typhoid  bacilli  increase  in 
number  in  sewage  but  slowly,  if  at  all;  consequently  that  they 
disappear  even  more  rapidly  than  a  general  analysis  would 
indicate. 

TABLE  No.  26e. 

AVERAGE    ANALYSES    OF    SEWAGE   OF   VARIOUS    CITIES    AND    TOWNS   IN 
MASSACHUSETTS    DURING    1908. 

(Parts  per  100,000). 


City  or  Town. 

Total 
Residue. 

Loss  on 
Ignition. 

Total. 

Ammonia. 

Chlorine. 

Oxygen 
Con- 
sumed. 
(Unfil- 
tered). 

Free. 

Albuminoid. 

Total. 

In 
Solution. 

Andover           . 

37-81 
133.62 

50-75 
24-32 
45-93 
44.64 

"7-93 
61.88 

39-43 
38.08 

45-44 
32-73 
41.60 

25-33 
89.78 

21.17 
82.46 
25.12 

i°-35 
18.16 

24-59 
72.54 
32-52 
18.77 

30-37 
19-59 
13.11 
22.25 
11.92 
5i.i5 

2.70 
7.07 
3.80 
1.18 

3-64 
6.28 
5-69 

5-02 

4.47 

2.90 

3-05 
1.87 

4.08 

o-99 
2.65 

0.56 
2.04 
0.68 
0.27 
0.62 
o-97 
i-55 
0.88 

o-S1 
0.65 
0.52 
0.26 
0.84 
0.24 
i-5i 

.22 

.42 

-33 

-14 

-37 
-45 
-53 
-35 

.22 

-23 
.21 

•13 

•33 
.08 

.94 

4.08 
14-89 
5-25 
3-°7 
7.69 
4.91 

12.20 
6.90 

5-33 
4-72 
6.38 
3-54 
5-29 
1.30 

6.44 

3-78 
24-37 
5-71 

i-79 

4.00 

5-74 
8.56 
6.17 
4-3° 

3-6* 
4.10 

2-47 

4.82 
1.79 

3i-58 

Brockton 

Clinton 

Concord       ... 

Framinghani 

Gardner*     ... 

Gardner"f"         .... 

Hopedale 

Leicester 

iMarlbo  rough 

Natick 

Pittsfield 

Spencer 

Stockbridge     .    ... 

West  borough  

Average  

55-28 

30.27 

3-69 

0.81 

-33 

6-13 

7-52 

*  Old  system. 


t  New  system. 


It  is  desirable  to  distinguish  between  aerobic,  anaerobic, 
and  facultative  bacteria,  and  between  the  liquefying  and  non- 
liquefying;  largely  because  of  the  effect  of  these  in  the  decomposi- 


382  SEWERAGE. 

tion  and  purification  of  sewage.  Also  to  ascertain  the  presence 
or  absence  of  B.  coli  communis,  especially  in  the  case  of  an  effluent 
from  a  purification  plant  where  a  high  percentage  of  bacterial 
removal  is  attempted  or  desirable. 

ART.  86.     POLLUTION  OF  STREAMS  AND  TIDAL  WATERS. 

The  simplest  solution  of  the  problem,  where  it  is  permis- 
sible, and  the  one  most  frequently  employed  in  this  county 
is  to  discharge  the  sewage  directly  into  some  flowing  stream 
or  large  body  of  fresh  water,  the  ocean  or  one  of  its  estuaries. 
This  is  called  "  disposal  by  dilution."  So  far  as  cheapness 
is  concerned  this  stands  easily  first  among  the  methods  of  dis- 
posal, since  it  requires  the  purchase  of  no  land  and  needs  no 
care  to  regulate  its  working,  excepting  where  the  discharge 
is  into  tidal  waters,  when  some  expense  is  frequently  gone 
to,  both  of  first  cost  and  of  maintenance,  to  regulate  the  time 
of  discharge.  It  is  usually  efficient  also  in  removing  the 
sewage  beyond  the  limits  of  the  area  contributing  to  its 
volume.  Looked  at  in  a  less  selfish  way,  and  considering  the 
good  of  the  State  and  country  as  well  as  of  the  locality 
sewered,  other  and  adverse  arguments  present  themselves  in  some 
cases.  Although  the  sewage  is  removed  to  a  distance  from  the 
contributing  territory  by  tides  or  currents,  it  may  be  deposited 
in  proximity  to  other  communities,  on  banks  or  shores  or 
retained  by  dams,  thus  creating  a  nuisance;  or  may  render 
unfit  for  drinking,  household,  or  manufacturing  purposes 
water  which  would  otherwise  be  so  used. 

The  effects  of  sewage  pollution  of  a  stream  in  creating  a 
nuisance  are  well  illustrated  by  the  Passaic  River. 

"The  great  extent  of  the  pollution  of  the  lower  Passaic 
may  be  illustrated  in  several  ways.  It  is  apparent  to  the  eye 
in  the  condition  of  the  river  during  the  summer;  in  the  foul- 


DISPOSAL    BY    DILUTION.  383 

-ness  of  the  shores  where  sewage-laden  mud,  when  exposed  to 
the  sun,  gives  out  foul  odors;  and  it  is  demonstrated  by  every 
practical  test.  The  cities  of  Newark  and  Jersey  City  have 
been  compelled  to  seek  water-supplies  elsewhere  at  large  ex- 
pense, and  the  immediate  decrease  in  zymotic  disease  in  these 
places  which  has  followed  the  change  has  shown  how  neces- 
sary it  is.  Fish  life,  excepting  of  a  few  hardy  kinds,  has  dis- 
appeared from  the  river,  and  fifteen  years  ago  shad,  which 
formerly  frequented  the  stream,  abandoned  it.  The  manu- 
facturers have  reported  that  the  acid  of  the  sewage-laden 
water  affected  boilers  so  as  to  make  its  use  inadvisable.  The 
use  of  the  river  for  pleasure  purposes,  which  at  one  time  made 
it  a  delight  to  thousands,  has  become  comparatively  infrequent, 
and  the  attractiveness  of  the  river  may  be  said  to  have  disap- 
peared." (Report  of  the  Passaic  Valley  Sewerage  Commission, 
1897.)  While  this  is  an  extreme  case,  there  are  many  others 
in  this  country  almost  as  bad  ;  and  as  the  country  becomes  more 
thickly  populated  other  streams  will  become  similarly  polluted. 
In  addition  to  pollution,  the  formation  of  deposits  may  become 
a  serious  matter.  In  the  case  of  storm  waters  more  or  less  sand 
and  heavy  silt  will  be  deposited  at  or  near  the  outlet  of  each  sewer 
and  it  may  even  become  necessary  to  remove  such  deposits  by 
dredging  at  intervals;  but  much  can  be  done  to  avoid  this  by 
discharging  into  rapid  currents.  In  the  case  of  house  sewage 
a  large  part  of  the  suspended  matter,  especially  the  soaps  and 
greasy  matter,  float  upon  the  surface,  but  a  considerable  part 
of  the  remainder  settles  to  the  lower  strata  and  is  deposited  at 
a  greater  or  less  distance  from  the  outlet.  Havana  harbor  is  an 
instance  of  deposit  of  this  kind,  there  being  several  feet  of  such 
deposit  over  a  considerable  portion  of  its  bottom.  Investigations 
which  have  not  been  completed  have  shown  New  York  harbor 
to  contain  as  much  as  10  or  1 5  feet  in  some  places  of  similar  sewage 
deposits.  Mr.  John  R.  Freeman,  in  reporting  upon  the  Charles 
river  dam,  cited  experiments  made  during  the  investigation  to 


SEWERAGE. 


show  that  sewage  matter  settles  much  more  quickly  in  salt  water 
than  in  fresh,  and  consequently  that  deposits  are  more  apt  to 
occur  near  the  outlet  when  sewage  is  discharged  into  the  ocean 
or  tidal  waters  than  when  into  rivers. 

The  amount  of  deposits  depends  to  a  considerable  degree 
upon  the  amount  and  rapidity  of  dilution,  and  it  therefore  seems 
desirable,  especially  where  discharge  is  into  salt  water,  to  locate 
the  outlet  near  the  line  of  maximum  motion  of  tide  or  current, 
and  to  employ  several  outlets  distributed  over  a  considerable 
area  when  the  amount  of  sewage  is  great. 

The  mortality  due  to  sewage-polluted  water  may  occur 
through  almost  any  enteric  disease,  but  the  greatest  is  prob- 
ably from  typhoid  fever.  An  illustration  of  the  mortality  from 
this  disease  due  to  sewage  is  found  in  the  city  of  Lawrence, 
Mass.,  which  uses  the  Merrimac  River  as  a  source  of  supply, 
which  river  receives  the  sewage  of  Lowell,  nine  miles  above. 
Since  August,  1893,  the  supply  has  been  filtered  and  the  result 
is  apparent  in  the  following  table. 

MORTALITY   FROM    TYPHOID   FEVER  IN    LAWRENCE,   MASS. 


Year  

1885 

1886 

1887 

1888 

1889 

1890 

1891 

1892 

1893 

Deaths       from 

typhoid  per 

100,000       in- 
habitants   

42 

57-5 

114.4 

113.6 

126.6 

134-4 

119.4 

105.2 

79.6 

Year  

1894 

1895 

1896 

1897 

1898 

1899 

1900 

1901 

1902 

Deaths   from 

* 

typhoid  per 

100,000     i  n  - 

habitants  

47-5 

30-7 

18.6 

16.2 

13-9 

33-» 

17-6 

i«.S 

17.6 

(See   also   Art.   9  of  the   author's  work  on   "Water-supply 
Engineering.") 

Another  illustration  was  the  epidemic  of  typhoid  fever  which, 


DISPOSAL    BY    DILUTION.  385 

in  the  winter  of  1898-99,  visited  two  or  three  cities  on  the  Passaic 
River  which,  for  a  few  days  when  the  supply  of  pure  water  ran 
low,  pumped  from  this  river  into  their  mains. 

In  this  connection  reference  should  be  made  to  the  danger  of 
spreading  certain  diseases  through  the  agency  of  oysters,  and 
that  of  the  destruction  of  fish  by  disposing  of  sewage  by  dilution. 
There  seems  to  be  little  doubt  that  typhoid  and  probably  other 
fevers  have  been  so  conveyed  by  oysters,  as  at  Wesleyan  University, 
Middletown,  Conn.,  in  1894,  and  again  in  1906  under  almost 
exactly  identical  circumstances;  and  at  Brightlingsea,  England, 
oysters  from  the  latter  place  being  accused  on  good  evidence  of 
having  caused  twenty-six  cases  of  typhoid  fever  in  1897.  These 
were  exposed,  however,  to  contact  for  hours  at  a  time,  at  low  tide, 
with  sewage  but  little  diluted.  In  view  of  this  and  of  similar  cases 
both  in  this  country  and  abroad,  Baltimore  decided  to  take  every 
precaution  in  the  way  of  sterilizing  its  sewage  in  order  to  protect 
the  important  oyster  industry  in  its  harbor. 

It  is  probable  that  germs  of  enteric  diseases  are  conveyed 
on  the  outside  rather  than  the  inside  of  the  body  of  the 
oyster,  and  that  there  is  little  danger  in  eating  sewage-fed 
fish  or  cooked  shellfish,  since  the  organic  matter  is  digested 
by  them  and  converted  into  healthy  tissue,  and  such  bacteria 
as  enter  the  digestive  organs  are  either  destroyed  or  leave  at 
once  in  the  excrement.  A  moderate  amount  of  fresh  organic 
matter  attracts  most  kinds  of  fish  which  live  upon  it  or  upon 
the  minute  animal  and  vegetable  life  of  which  it  forms  the 
food;  but  the  gases  of  putrefaction  are  poisonous  to  animal  life. 

ARTICLE  87.    AIMS  OF  TREATMENT. 

The  aim  of  any  treatment  of  sewage  may  be  either  to  pre- 
vent the  creation  of  a  nuisance,  or  to  produce  an  effluent  which, 
if  discharged  into  a  river,  will  not  render  it  unsuitable  for  city 
water  supplies.  The  former  case  may  exist  where  the  sewage 


386  SEWERAGE 

is  discharged  into  a  stream,  a  lake  or  salt  water;  the  latter 
where  into  potable  fresh  water  only.  A  third  case  is  found 
in  many  coast  cities  where  shellfish  are  raised  or  fattened  for 
the  market;  which  shellfish  might  serve  as  carriers  of  disease 
germs. 

The  purification  must  be  considered  from  both  the  chemical 
and  the  bacteriological  sides.  For  either  of  these  a  standard  of 
purity  for  either  the  first  or  the  second  aim  is  most  difficult  to 
decide  upon;  and  although  a  number  of  standards  have  been 
advanced  and  some  are  still  used  in  other  countries,  it  does  not 
seem  probable  that  a  general  chemical  standard  will  ever  be 
adopted.  It  is  possible,  however,  that  a  bacteriological  one  may 
be  reached,  applicable  to  cases  where  potability  or  oyster  con- 
tamination is1  an  important  consideration.  The  Royal  Com- 
mission of  England  in  1909  stated,  as  a  chemical  standard,  that 
an  effluent  would  generally  be  satisfactory  for  discharge  into  a 
stream,  if  it  complied  with  the  following  conditions : 

(i)  That  it  should  not  contain  more  than  three  parts  per  100,000  of  sus- 
pended matter;  and  (2)  that  after  being  filtered  through  filter  paper  it  should 
not  absorb  more  than  (a)  0.5  parts  by  weight  per  100,000  of  dissolved  or  atmos- 
pheric oxygen  in  twenty-four  hours;  (6)  i.o  part  by  weight  per  100,000  of 
dissolved  or  atmospheric  oxygen  in  forty-eight  hours,  or  (c)  1.5  parts  by  weight 
per  100,000  of  dissolved  or  atmospheric  oxygen  in  five  days. 

Where  it  is  desired  only  to  prevent  a  nuisance,  the  bacteriolog- 
ical condition  need  hardly  be  considered.  In  such  a  case  also  the 
purification  need  be  carried  to  such  a  point  only  that  a  large 
percentage  of  all  matters  in  suspension  are  removed  or  so  modified 
that  the  danger  of  future  putrefaction  is  averted. 

The  maintaining  of  a  river  water  potable,  however,  calls  for 
a  much  higher  standard.  To  be  absolutely  safe  it  would  seem, 
from  our  present  knowledge,  that  all  bacteria  should  be  removed, 
since  we  are  not  certain  that  some  of  those  escaping  are  not 
pathogenic.  The  removal  of  99.98%  of  the  bacteria,  however, 
probably  reduces  the  chance  of  infection  by  at  least  that  amount; 


DISPOSAL  BY   DILUTION  387 

and  if  the  effluent  be  then  diluted  with  ten  times  its  volume  of 
pure  water,  the  chance  of  infection  by  drinking  such  dilution 
would  be  about  1/50,000  of  that  by  drinking  the  sewage.  Where 
this  is  the  aim  the  standard  for  the  number  of  bacteria  permissible 
in  the  effluent  should  be — the  least  which  the  state  of  the  art 
renders  possible. 

It  is  now 'possible  to  almost  completely  sterilize  sewage,  and 
thus  to  deliver  an  effluent  of  a  very  high  bacterial  standard. 
Except  for  reasons  to  be  referred  to  later,  such  disinfection  (in- 
complete sterilization)  should  follow  rather  than  precede  any 
biological  treatment,  since  a  considerable  percentage  of  the  con- 
tained bacteria  are  necessary  for  the  liquefying  and  oxidation 
of  the  organic  matter  in  the  sewage.  Even  complete  steriliza- 
tion will  not  prevent  such  liquefying  and  oxidation,  but  will  delay 
it  and  will  probably  result  in  later  putrefaction  if  other  treatment 
has  not  effected  sufficient  removal  of  the  organic  matter.  Con- 
sequently, sterilizing  to  avoid  decomposition  should  not  be  at- 
tempted, since  decomposition  must  precede  any  purification, 
and  in  most  cases  the  sooner  it  occurs  the  better.  Disinfection 
to  remove  pathogenic  bacteria  is  especially  applicable  where  the 
effluent  is  discharged  near  shellfish  beds,  or  under  other  condi- 
tions where  bacteriological  purification  is  more  important  than 
organic. 

The  question  of  the  degree  of  purification  demanded  in  any 
specific  case  is  one  more  of  State  law  or  the  policy  of  State  Health 
Boards  than  of  engineering;  but  it  deserves  some  mention  at 
this  point.  The  question  is  being  debated  whether  it  is  desirable 
to  compel  cities  to  so  purify  their  sewage  that  those  below  can 
use  the  streams  receiving  the  same  for  drinking-water  without 
further  treatment;  or  whether  the  mere  prevention  of  a  nuisance 
by  sewage  effluents  should  be  the  extent  of  requirement.  The 
former  idea  is  based  largely  on  the  hypothesis  that  morally  the 
city  has  no  right  to  pollute  a  stream  and  thus  put  another  city  to 
the  expense  of  purifying  it  for  public  use.  On  the  other  hand 


388  SEWERAGE. 

it  is  claimed  that  the  occasional  lapses  in  efficiency  of  the  sewage 
purification  plants  which  are  probable,  and  especially  the  existence 
of  other  sources  of  pollution  which  are.  well-nigh  unpreventable, 
make  it  necessary  for  a  city  to  purify  any  river  water  used  as  a 
public  supply;  and  this  being  the  case  it  deducts  very  little,  if 
anything,  from  the  expense  of  water  purification  to  secure  high 
bacterial  purity  in  sewage  effluents.  Consequently  there  seems 
to  be  little  question  that  the  combined  expense  of  sewage  and 
water  purification,  to  all  cities  located  upon  a  river  into  which 
all  discharge  sewage  and  from  which  all  obtain  their  water  sup- 
plies, would  be  less  with  partial  sewage  purification  than  if  this 
were  made  complete;  and  at  this  writing  (1910)  the  general 
tendency  is  towards  the  prevention  of  nuisance  only;  but  on  the 
other  hand,  strenuous  and  intelligent  efforts  are  being  made  to 
.actually  obtain  a  general  enforcement  of  such  treatment  of  all 
sewage.  This  means  that  the  number  of  sewage  purification 
plants  is  being  greatly  increased,  but  that  the  efficiency  demanded 
has  been  placed  much  lower  than  heretofore. 

The  difficulty  of  setting  a  general  standard  to  be  met  by  all 
sewage-disposal  plants  lies  not  only  in  the  various  requirements 
to  be  met,  but  also  in  the  varying  characteristics  of  both  the  sewage 
and  the  stream  which  receives  it.  Where  the  stream  is  small 
a  much  higher  degree  of  purification  is  necessary  to  prevent  a 
nuisance  than  where  it  is  large.  Moreover,  the  amount  of  free 
oxygen  in  the  stream  is  an  important  consideration.  The  scientific 
method  would  be  to  ascertain  the  amount  of  free  oxygen  in  the 
diluting  stream  passing  the  effluent  outlet  per  second,  and  to 
permit  no  more  unoxidized  organic  matter  to  reach  such  stream 
per  second  than  can  be  fully  oxidized  by  J  or  }  of  this  amount 
of  oxygen  (since  the  intermingling  of  sewage  and  stream  probably 
will  not  be  complete) .  So  far  as  all  organic  matter  except  bacteria 
is  concerned,  the  above  standard  would  also  insure  a  safe  potable 
water  if  time  and  opportunity  for  complete  intermingling  and 
oxidation  be  afforded. 


DISPOSAL    BY    DILUTION.  389 

In  examining  a  stream  for  sewage  pollution  it  should  be 
remembered  that  the  presence  of  chlorine  in  excess  of  the  local 
normal  is  generally  an  indication  of  sewage  pollution;  nitrates 
indicate  the  amount  of  organic  matter  rendered  innocuous;  and 
albuminoid  ammonia  is  taken  as  an  index  of  the  polluting  organic 
matters  still  present.  Numerous  bacteria  are  not  necessarily 
indicative  of  sewage  pollution,  but  B.  coli  are  generally  assumed 
to  be  (although  small  numbers  may  have  been  voided  by  animals 
other  than  man).  The  character  of  an  effluent  should  not  be 
judged  by  its  appearance  alone,  by  its  chemical  or  bacteriological 
analyses,  but  by  the  three  combined;  since  it  may  be  clear,  but 
contain  many  pathogenic  bacteria  or  dissolved  matter  which 
may  be  precipitated  or  putrefy  and  create  a  nuisance; 
also  a  turbid  effluent  may  contain  only  mineral  matters  or  such 
organic  ones  as  are  harmless  and  will  undergo  no  change  but 
oxidation.  V 

ARTICLE  88.    DISPOSAL  BY  DILUTION. 

There  are  undoubtedly  conditions  under  which  disposal  by 
dilution  is  much  less  objectionable  than  any  other  available  method. 
And  in  considering  this  it  must  be  borne  in  mind  that  the  liquid 
must  ultimately  be  discharged  into  some  stream  or  body  of  water; 
the  question  being  therefore  to  what  extent,  if  at  all,  must  it  be 
purified  or  modified.  Under  what  conditions  and  to  what  extent 
a  water  receiving  sewage  will  purify  itself  is  a  question  which  has 
received  less  attention  than  have  methods  of  treating  sewage, 
although  it  is  much  the  most  common  method  of  disposal.  The 
self-purification  may  be  considered  as  to  the  organic  matter  and 
as  to  the  bacteria.  (Sand  and  other  mineral  suspended  solids 
cause  shoaling  near  the  mouth  of  a  sewer,  unless  this  be  in  a  swift 
current.  But  the  treatment  of  this  problem  has  already  been 
considered;  catch-basins  or  occasional  dredging  being  the  most 
common  solutions). 


39°  SEWERAGE. 

Considering  first  the  organic  matter,  the  agents  of  purification 
are  sedimentation  and  dilution,  accompanied  and  followed  by 
liquefaction  and  oxidation;  and  the  agency  of  animal  and  vegetable 
life.  Any  considerable  amount  of  sedimentation  is  objectionable, 
especially  if  concentrated  in  a  limited  area;  because  the  matter 
deposited  undergoes  putrefaction,  and  the  products  of  this  are 
disagreeable  and  render  the  water  above  unsuitable  for  a  public 
supply  if  they  do  not  even  create  a  nuisance.  If  the  deposit  is 
thin,  however,  the  products  of  putrefaction,  both  liquid  and  gas- 
eous, may  be  so  small  in  quantity  that  they  are  rapidly  oxidized 
by  the  water  above.  This  will  depend  upon  the  relative  amounts 
of  putrefaction  products  and  of  oxygen  available  per  day  or  hour 
in  the  water  above. 

By  dilution,  or  intermingling  of  the  sewage  with  large  quan- 
tities of  water,  the  ratio  of  available  oxygen  in  the  water  to  organic 
matter  may  be  made  sufficient  to  cause  the  rapid  oxidation  of 
all  the  nitrogenous  matter  before  sedimentation  occurs.  Such 
dilution  prevents  putrefaction;  but  total  reduction  to  nitrates 
by  oxidation  is  in  general  slower  than  by  combined  anaerobic 
and  aerobic  action.  It  is  the  opinion  of  many  experts  that  still 
water  purifies  itself  more  rapidly  than  flowing,  because  of  the 
liquefaction  taking  place  in  sediment,  which  is  deposited  more 
abundantly  in  still  water.  The  chief  advantage  possessed  by 
running  water  is  that  the  constant  delivery  of  fresh  water  insures 
a  constant  mixture  and  completeness  of  diffusion  not  secured  by 
discharge  at  one  point  in  quiet  water.  But,  as  Mr.  X.  H.  Good- 
nough  has  said  in  a  report  to  the  Charles  River  Dam  Committee : 
"The  sewage  discharged  into  a  pond  or  stream  may  be  objection- 
able or  not,  in  the  neighborhood  of  the  outlet,  depending  upon  the 
location  of  the  outlet  with  reference  to  the  stream  or  pond,  and  the 
conditions  in  the  neighborhood.  Observations  upon  the  dis- 
charge of  sewage  into  water  at  many  places  show  that  there  is  much 
advantage  in  discharging  it  at  several  outlets,  since  the  sewage 
then  mingles  much  more  rapidly  with  the  water,  and  is  subjected 


DISPOSAL    BY    DILUTION.  391 

more  quickly  to  those  actions  which  tend  to  remove  its  effect." 
''Experience  at  places  at  which  sewage  is  discharged  into  a  pond 
or  slowly  moving  stream  indicates  that  sewage  discharged  into 
such  bodies  of  water  has  a  less  noticeable  effect  upon  their  waters 
than  an  equal  quantity  of  sewage  has  upon  a  rapidly  moving 
stream  of  equivalent  volume." 

The  above  does  not  refer  to  stagnant  water,  since  there  must 
be  continually  fresh  quantities  of  oxygen  available  in  the  water 
of  dilution.  This  may  be  supplied  in  a  large  body  of  water  by 
absorption  of  oxygen  from  the  air  into  the  surface  layers  of  water, 
combined  with  a  continual  vertical  circulation  of  water  due  to 
differences  in  temperature  or  to  winds.  But  these  causes  are  less 
reliable  than  a  constant  but  slow  translation  as  by  stream  flow 
or  tidal  currents.  Under  any  condition  the  organic  matter  must 
come  in  contact  with  sufficient  oxygen  to  permit  mineralization, 
before  putrefaction  products  reach  the  surface  of  the  stream,  if 
a  nuisance  is  to  be  avoided.  No  matter  how  large  the  volume 
of  diluting  water,  unless  the  current  at  the  immediate  outlet  be 
sufficiently  swift  to  effect  rapid  and  thorough  diffusion  and  mix- 
ing, local  nuisance  will  be  caused  by  the  discharge  of  large  volumes 
of  sewage  at  one  point  which  might  be  entirely  avoided  by  provid- 
ing several  outlets  some  distance  apart.  A  large  volume  of  sewage 
discharged  from  a  single  outlet  into  a  stream  or  lake  can  frequently 
be  traced  by  its  color  for  a  long  distance,  only  slowly  mixing  at 
its  edges  with  the  purer  water. 

While  rapid  diffusion  and  intimate  intermingling  are  necessary, 
tthe  degree  of  rapidity  depends  partly  upon  the  putrescibility  of 
the  sewage;  a  corollary  to  which  is  that  the  amount  of  sewage 
which  a  given  volume  of  flow  will  receive  without  nuisance  is 
similarly  dependent.  Certain  processes  of  sewage  treatment 
produce,  as  their  chief  effect,  reduced  or  delayed  putrescibility; 
the  most  important  being  the  sprinkling  or  trickling  filter. 

It  is  apparent  that  the  amount  of  flow  of  a  diluting  stream  re- 
quired to  inoffensively  dispose  of  a  given  volume  of  sewage  de- 


392  SEWERAGE. 

pends  upon  the  strength  and  putrescibility  of  the  sewage,  the 
available  oxygen  in  the  water,  conditions  favoring  sedimentation 
or  rapid  intermingling,  diversity  of  outlets  and  other  conditions. 
The  limits  are  placed  by  most  authorities  at  between  1,500  gallons 
and  4,000  gallons  per  day  per  capita  contributing  sewage.  (The 
proportion  is  sometimes  stated  in  terms  of  cubic  feet  or  gallons 
of  sewage,  but  since  the  amount  of  impurity  is  not  increased  by 
greater  per  capita  consumption  or  waste  of  water,  the  former 
method  seems  preferable.)  That  is,  most  agree  that  below  the 
minimum  a  nuisance  is  pretty  sure  to  be  occasioned;  and  with  a 
dilution  above  the  maximum  it  would  be  almost  certainly  avoided. 
This  means  that  this  amount  of  water  must  not  only  be  flowing 
past  the  sewer  outlet,  but  must  be  mixed  with  the  sewage.  It  is 
quite  possible  to  have  a  local  nuisance  created,  in  the  form  of 
nauseous  gases  and  floating  matter,  by  failure  to  effect  rapid 
mixing,  but  to  have  a  rapid  reduction  to  inoffensive  and  harmless 
conditions  after  the  mixing  had  taken  place.  This  reduction, 
by  oxidation,  is  a  function  of  time  rather  than  of  distance  traveled 
by  the  stream,  and  this  furnishes  an  additional  advantage  for 
discharge  into  slowly  moving  streams,  in  that  the  effect  of  the 
sewage  does  not  extend  so  far.  Two  or  three  hours  after  thorough 
intermingling  are  frequently  sufficient  for  the  reduction  of  much 
of  the  nitrogenous  matter  into  nitrates. 

It  should  be  remembered  that  the  water  of  dilution  has  been 
considered  in  the  above  discussion  to  be  unpolluted;  and  that  the 
same  water,  swinging  back  and  forth  with  the  tide  past  a  sewer 
outlet,  will  soon  become  grossly  polluted.  The  actual  dilution* 
will  be  closely  indicated  by  multiplying  the  actual  cross-sectional 
area  of  the  channel  by  the  distance  separating,  the  positions 
occupied  by  a  given  float  at  two  successive  ebb  tides,  as  compared 
with  the  sewage  discharged  in  the  same  time.  There  will,  how- 
ever, be  a  somewhat  greater  reduction  of  the  sewage  than  is 
indicated  by  such  a  calculation,  since  the  water  will  continu- 
ally absorb  fresh  oxygen  from  the  air  above  and  sedimenta- 


DISPOSAL    BY    DILUTION.  393 

tion  will  continue  to  remove  sewage  matter,  and  more  com- 
plete intermingling  will  assist  in  oxidation  and  diminish  the 
possible  nuisance  by  mere  physical  dilution.  Thus  the  same 
volume  of  water,  moving  back  and  forth  with  the  tide  and 
receiving  no  fresh  pollution,  will  continually  improve  in 
character. 

Sedimentation  is  most  active  when  clay,  sand  or  other  heavy 
matter  is  carried  in  the  sewage;  this,  in  sinking,  carrying  with 
it  other  finer  and  lighter  matter,  including  bacteria.  A  rough 
bottom,  shallow  water  and  high  velocity,  each  and  especially 
all  combined,  interfere  with  sedimentation,  but  assist  in  inter- 
mingling. It  is  found  that  sedimentation  is  much  more  rapid 
in  salt  water  than  in  fresh;  consequently  more  attention  should 
be  paid  to  the  location  of  outlets  in  the  former,  to  insure  their 
discharging  into  rapid  currents  or  in  small  quantities  through 
numerous  outlets.  Mr.  H.  W.  Clark,  Chemist  to  the  Massachu- 
setts State  Board  of  Health,  found  that  "temperatures  and  other 
conditions  being  equal,  salt  water  apparently  holds  less  oxygen 
in  solution  than  fresh  water.  This  being  so,  it  is  evident  that, 
volume  for  volume,  fresh  water  can  receive  the  greater  amount 
of  pollution  without  the  exhaustion  of  its  oxygen,  if  bacterial 
life  is  of  equal  vigor  in  each  case."  Also  the  odors  given  off  by 
putrefying  sewage  in  salt  water  are  greater  than  when  in  fresh. 

Investigations  of  New  York  Harbor  made  by  the  Metropolitan 
Sewerage  Commission  showed  that  at  all  points  at  all  distant  from 
sewer  outlets  most  of  the  sewage  was  either  floating  in  the  top 
six  inches  or  had  settled  to  the  bottom;  which  indicates  that 
surface  area  is  more  important  than  depth  in  salt-water  dilution. 
From  experiments  conducted  by  the  Metropolitan  Sewerage 
Commission  in  1896  in  Boston  Harbor,  where  sewage  is  stored 
and  discharged  on  the  ebb-tide  and  in  addition  about  the  same 
amount  is  discharged  continuously,  it  was  found  that  the  area 
covered  by  a  reservoir-discharge  in  three-quarters  of  an  hour  of 
22,000,000  gallons  is  approximately  750  acres;  but  when  but 


394  SEWERAGE. 

11,000,000  gallons  is  discharged  at  once  this  area  is  not  more  than 
250  acres.  In  calm  weather  the  sewage  is  offensively  visible 
over  two-thirds  of  this  area,  but  the  odors  are  confined  to  a  rela- 
tively small  portion.  By  far  the  greatest  amount  of  sewage  is 
found  in  the  upper  two  or  three  inches  of  the  polluted  area,  and 
this  largely  disappears  in  two  or  more  hours  after  the  discharge, 
depending  chiefly  upon  the  force  of  the  waves.  A  thin  film  of 
grease  sometimes  covers  large  areas,  but  is  not  accompanied  by 
enough  sewage  to  be  detected.  Within  the  polluted  area  sewage 
cannot  be  detected  at  a  greater  depth  than  5  feet  at  the  outlet 
and  2  feet  near  the  edges  of  the  area.  When  35,000,000  to  40,- 
000,000  gallons  daily  was  continuously  discharged  the  dilution 
was  such  that,  15  minutes  after  leaving  the  outlet,  sewage  con- 
stituted but  20  per  cent  of  the  surface  water;  30  minutes  after, 
15  per  cent;  45  minutes  after,  5  per  cent;  and  60  minutes  from 
the  outlet  but  4  per  cent  of  the  surface-water  was  sewage.  The 
discoloration  was  evident  for  about  ij  miles,  and  covered  about 
350  acres  during  ebb-tide  and  300  acres  during  flood-tide.  The 
observations  indicate  that,  the  greater  the  quantity  of  sewage 
that  is  discharged  the  greater  is  the  area  covered,  the  area  increas- 
ing in  more  than  direct  proportion  to  the  sewage  discharged. 
This  is  additional  reason  for  discharging  at  a  number  of 
outlets. 

The  two  outlets  in  Boston  offer  an  illustration  of  the  compara- 
tive merits  of  continuous  and  ebb-tide  discharge.  "The  great 
advantage  of  discharging  sewage  continuously  and  in  compar- 
atively small  quantities  into  a  large  volume  of  tide  water,  as  com- 
pared with  discharging  it  in  large  quantities  from  reservoirs  in 
a  limited  time,  is  well  illustrated  by  a  comparison  of  the  condi- 
tions at  the  present  outlets  at  Moon  Island  and  at  Deer  Island. 
At  Moon  Island  a  large  area  is  covered  densely  with  sewage  dur- 
ing a  period  of  several  hours  at  each  tide,  while  at  Deer  Island 
the  sewage  flows  in  different  directions  at  different  parts  of  the  day, 
covers  a  much  smaller  area  and  becomes  more  readily  broken 


DISPOSAL   BY    DILUTION.  395 

up  and  mingled  with  the  sea  water."     (Report  of  Mass.  State 
Board  of  Health  on  Boston  Harbor). 

In  the  case  of  discharge  into  large  lakes,  there  are  no  tides 
to  assist  in  diffusion,  and  currents  and  winds  are  the  chief  agents. 
Sedimentation  is  less  active  than  in  salt  water,  and  sewage  pollu- 
tion has  often  been  traced  for  five  to  ten  miles  from  an  outlet. 
As  in  the  case  of  salt  water,  the  distance  reached  by  unoxidized 
.sewage  seems  to  increase  more  rapidly  than  the  amount  discharged. 
In  general  the  same  principles  hold;  that  numerous  outlets  at 
some  distance  from  shore  are  desirable  to  prevent  a  nuisance. 

Organic  matter  in  water  forms  the  food  of  filth  infusoria, 
hydra,  rotifera,  entomostracan  Crustacea,  fresh-water  shrimp, 
and  the  larvae  of  a  number  of  water  insects.  Entomostraca 
seem  to  be  the  most  efficient  in  the  purification  of  streams,  and 
thrive  on  human  excrement.  A  sewage-polluted  river  may  con- 
tain 25  to  50  or  more  per  gallon;  but  when  the  pollution  becomes 
intense  they  seem  to  disappear,  probably  because  of  lack  of 
oxygen,  but  their  place  is  taken  by  larvae.  Diatoms,  desmids, 
confervoid  algae  and  other  vegetable  organisms,  together  with 
bacteria,  act  largely  upon  the  dissolved  impurities;  although  the 
last-named  seem  to  attack  organic  matter  also.  These  all  serve 
as  food  for  fish;  and  fish,  in  turn,  for  man;  and  sewage  matter 
disposed  of  by  dilution  is  therefore  not  wasted,  although  it  does 
not  serve  as  fertilizer  for  plant  life. 

Seaweed  plays  an  important  part  in  the  purification  of  tidal 
water.  The  Royal  Commission  (England)  found  that  the  green 
seaweeds  assimilate  nitrogenous  compounds  such  as  ammonia 
and  nitrates,  and  also  evolve  large  quantities  of  oxygen.  They 
are  thus  of  great  value  in  the  purifying  of  sewage-laden  waters. 
When  thrown  upon  the  shore  by  storms  they  give  off,  in  decompos- 
ing, quantities  of  sulphuretted  hydrogen,  which  can  be  avoided 
by  gathering  up,  drying  and  burning  them. 

Certain  fish  eat  directly  organic  matters  in  sewage,  when 
this  is  discharged  fresh  into  running  water,  which  is  not  therefore 


396  SEWERAGE. 

deprived  of  oxygen  at  the  sewer  mouth.  But  as  intermingling 
takes  place  and  oxygen  is  taken  up  by  the  sewage  conditions 
become  unfavorable  to  fish  life;  and  few  fish  can  live  in  highly 
polluted  waters.  This  is  generally  because  of  lack  of  oxygen; 
but  some  trade  wastes  contain  acids  and  others  gelatinous  or 
colloidal  matters  which  collect  around  the  gills  and  prevent 
breathing. 


CHAPTER  XVI. 
METHODS   OF   TREATMENT. 
ARTICLE  89.     GENERAL  PRINCIPLES. 

THE  methods  of  treating  sewage  may,  in  conformity  with  the 
ideas  previously  stated,  be  classified  as  those  for  effecting  physical 
removal  of  suspended  matter,  chemical  change  in  organic  matter, 
physical  removal  of  bacteria,  destruction  of  bacteria  by  chemicals 
or  for  the  biological  destruction  of  both  organic  and  bacterial 
matter. 

Physical  removal  of  suspended  matter  is  effected  by  straining 
out  the  coarser  matters  by  screens,  by  sedimentation,  by  surface 
adhesion,  and  by  precipitating  by  adding  a  coagulant.  Some 
chemical  change  generally  accompanies  coagulation;  but  such 
change  is  not  the  chief  aim  of  any  process  which  has  been  adopted 
in  practice;  although  some  have  been  suggested,  such  as  oxidation 
of  organic  matter  by  permanganates.  There  is  a  change  which 
might  perhaps  be  called  structural  rather  than  chemical,  and 
which  has  been  termed  "modification"  of  organic  matter,  which 
renders  this  less  subject  to  putrefaction,  although  little  chemical 
change  can  be  detected  except  by  the  most  delicate  tests.  The 
change  makes  it  possible  to  discharge  the  matter  into  a  stream 
without  creating  a  nuisance  (other  than  such  as  would  be  created 
by  an  equal  amount  of  surface  soil  from  a  field),  where  otherwise 
a  nuisance  would  be  inevitable. 

More  or  less  physical  removal  of  bacteria  is  effected  by  any 
removal  of  suspended  matter,  since  the  bacteria  exist  largely  in 
and  on  such  matter.  Filters  also  remove  bacteria  directly  by 
surface  adhesion,  and  partly  by  straining  when  covered  with  a 
dense  "schmutzdecke."  Sterlizing  agents  destroy  the  life  of 
bacteria;  and  heat  might  theroretically  be  used  for  this  purpose, 

397 


39 8  SEWERAGE. 

but  no  method  has  been  devised  for  making  this  commercially 
practicable.  Bacteria  removed  from  their  habitat  or  deprived 
of  sustenance  will  in  time  die;  although  some  spores  can  retain 
the  germ  of  life  indefinitely  under  adverse  conditions.  However, 
disease  germs  do  not  assume  the  spore  condition. 

In  all  lifeless  organic  matter  there  exist  countless  bacteria 
whose  function  it  is  to  break  down  the  organic  structure  and  re- 
solve the  matter  into  simpler  forms.  One  class  change  the  nitrog- 
enous matter  into  readily  oxidizable  forms,  and  the  resulting 
mineral  compounds  are  the  final  stage  of  thorough  purification; 
the  next  stage  of  which,  in  nature's  cycle,  would  be  their  absorp- 
tion by  plant  life  as  food.  " Biological  disposal"  methods  are 
efforts  to  intensify  this  action  as  to  both  time  and  space.  Such 
destruction  of  objectionable  bacteria  as  is  effected  by  biological 
action  is  probably  due  largely  to  the  creation  of  adverse  conditions. 

There  is  probably  no  method  of  sewage  treatment  in  use 
to-day  which  does  not  combine  two  or  more  of  the  above  proc- 
esses, unless  it  may  be  disinfection.  But  each  is  best  adapted 
to  most  economically  or  effectively  maintain  one  of  them,  the  others 
being  in  a  measure  incidental,  or  carried  on  uneconomically. 
The  effort  should  be  to  determine  just  what  method  or  combina- 
tion of  methods  would  most  economically  produce  the  desired 
results,  consideration  being  had  of  local  conditions  and  possibil- 
ities and  the  character  of  the  sewage. 

In  studying  the  subject,  thought  must  be  given  to  the  ultimate 
disposal  of  all  the  objectionable  matter.  All  methods  (except 
mere  disinfection)  results  in  an  accumulation  in  the  plant  of  more 
qr  less  of  the  suspended  matter,  which  is  of  varying  degrees  of 
offensiveness  depending  upon  the  process;  and  this  must  be  in 
some  way  disposed  of.  Moreover,  the  oxidized  organic  matter 
(nitrates  and  nitrites)  are  rich  plant  food,  and  although  they  are 
harmless  they  may  lead  to  an  undesirable  growth  of  vegetable 
matter  in  the  water  which  receives  them. 

Certain  methods  and  apparatus  are  best  adapted  to  the  coarse 


METHODS    OF    TREATMENT.  399 

work  of  removal  of  gross  suspended  matters;  others  to  the  mod- 
ification of  organic  matters;  others  to  biological  liquefaction; 
still  others  to  biological  oxidation.  The  last  are  uneconomical 
contrivances  for  effecting  the  purposes  of  the  first;  and,  theoret- 
ically at  least,  the  greatest  efficiency  in  the  plant  as  a  whole  is 
obtained  by  performing  the  rough  work  by  some  rapid  clarifica- 
tion process,  and  the  finishing  purification  (when  necessary) 
by  the  more  sensitive  aerobic  filter.  But  the  available  area  and 
materials,  character  of  sewage,  fall  available,  etc.,  may  outweigh 
these  purely  theoretical  conditions.  Moreover,  the  combining 
of  the  two  general  functions  in  one  appliance,  although  one  of 
them  may  be  effected  uneconomically,  may  produce  an  economy 
of  combined  action  greater  than  would  be  possible  by  two  ap- 
pliances or  operat'ons,  because  of  the  complication  of  operations 
thus  introduced. 

The  general  structures  and  appliances  for  treating  sewage 
consist  of  strainers  for  removing  coarse  suspended  matters;  tanks 
for  sedimentation;  septic  tanks  for  developing  septic  action  in 
.sediment;  the  treatment  of  sewage  with  coagulants  to  hasten  and 
increase  precipitation;  "hydrolytic"  and  Emscher  tanks  for 
utilizing  surface  adhesion  in  clarifying  sewage  and  for  securing 
more  advantageous  septic  action;  filters  of  coarse  material — • 
contact  filters —  for  removing  suspended  matter  by  surface  adhesion 
and  incidentally  by  straining,  together  with  bacterial  action  upon 
the  organic  matter  so  removed ;  other  coarse-grain  filters  in  which 
suspended  organic  matter  removed  by  surface  adhesion  is  so 
modified  as  to  be  non-putrescible — sprinkling  or  trickling  filters; 
fine-grain  filters  in  which  straining  and  surface  adhesion  remove 
a  large  part  of  the  suspended  organic  matter  and  also  bacteria, 
and  produce  a  large  amount  of  purification  by  oxidation;  the 
irrigation  of  cultivated  land  with  sewage;  treatment  with  dis- 
infectants to  kill  off  most  of  the  bacteria,  together  with  some  other 
contrivances  and  processes  advocated  for  various  purposes  but 
not  in  common  use. 


400  SEWERAGE. 

ART.  90.     STRAINING. 

All  processes  of  purification  involve  the  removal  from  sewage 
of  suspended  matter;  and  some  of  this  must  be  removed  before 
pumping  to  protect  the  pumps.  The  coarsest,  such  as  sticks, 
rags,  paper  and  kitchen  refuse  is  removed  by  screens.  Coke  or 
other  coarse-grain  filters  are  sometimes  used  for  removing  these 
and  smaller  matters  also.  Sedimentation  in  tanks  will  remove 
a  large  part  of  all  but  colloidal  matters,  and  more  or  less  of  these, 
The  amount  and  rapidity  of  sedimentation  may  be  increased 
by  introducing  coagulants.  The  removal  of  colloidal  matters  has 
been  increased  by  constructing  in  a  tank  a  number  of  vertical 
surfaces  to  which  such  matters  adhere,  falling  off  from  time  to 
time  in  large  flakes.  Tanks  have  been  built  containing  large 
numbers  of  horizontal  surfaces,  placed  a  few  inches  apart  vertically, 
on  which  suspended  matters  collect.  Other  tanks  are  filled  with 
stones  or  sand  which  remove  suspended  matter  partly  by  strain- 
ing and  partly  by  surface  adhesion.  In  each  kind  of  tanks  other 
processes  are  undergone  by  the  sewage,  which  will  be  discussed 
separately. 

When  the  sewage  is  to  be  treated  on  any  kind  of  filter  the 
previous  removal  of  coarse  suspended  matter  is  more  important 
than  is  generally  appreciated.  "The  volume  of  sewage  which 
may  be  successfully  purified  upon  a  given  filter  area  is  inversely 
proportional  to  the  amount  of  suspended  matters  in  the  sewage 
applied.  In  other  words,  if  the  whole  or  a  part  of  the  suspended 
matters  are  removed  form  the  sewage  by  some  treatment  pre- 
liminary to  filtration,  the  filters  can  be  operated  at  much  greater 
rates  and  a  smaller  area  will  be  required  for  treatment  of  a  given 
volume  of  sewage."  (Report  of  Mass.  State  Board  of  Health, 
1908.) 

The  simplest  strainers  are  of  rods  or  wire  screens  of  galvanized 
iron,  copper,  etc.  Screens  are  generally  placed  vertically  be- 
tween the  sewer  outlet  and  the  tank  or  filter,  or  the  pump  suction. 


METHODS   OF    TREATMENT.  401 

As  strainers  generally  become  clogged  by  suspended  matter  some 
method  of  cleaning  them  must  be  provided,  either  by  removing 
them,  washing  by  a  stream  of  water  applied  by  a  hose,  or  in 
some  other  way.  If  the  screen  is  of  fine  mesh,  a  perforated 
plate  may  be  used  as  a  screen,  which  can  be  cleaned  by  passing 
a  squeegee  over  its  surface.  The  iron  rods  used  in  this  country 
are  generally  round,  J  to  J  inch  in  diameter  and  spaced  with 
J-  to  f-inch  clear  opening,  although  the  spacing  has  been  as  great 
as  6  inches.  Rod  strainers  are  placed  either  vertical  or  inclined 
as  much  as  45°  from  the  vertical.  Material  can  be  removed 
from  them  with  rakes,  and  they  are  cleaned  more  easily  than  are 
screens,  but  are  not  so  effective. 

Screens  of  square  or  of  diamond  mesh,  when  used,  should 
"be  provided  in  duplicate  in  order  that  one  set  may  be  in  use  when 
another  is  being  cleaned.  Experiments  were  made  at  Columbus, 
O.,  in  1905  upon  various  kinds  and  meshes.  Square  mesh  screens 
of  o.375-inch  clear  opening  caused  trouble  as  to  both  durability 
and  readiness  of  cleaning.  Quarter-inch  vertical  rods  with  J- 
inch  clear  openings  were  too  coarse,  and  when  the  opening  was 
reduced  to  -J  inch  it  was  found  difficult  to  clean.  Diamond 
mesh  wire  screen,  woven  of  No.  12  wire,  was  finally  adopted, 
the  clear  mesh  opening  being  J  inch;  followed  by  a  screen  for 
second  screening  with  f-inch  mesh.  By  these  0.17  cu.yds.  of 
coarse  matter  was  removed  per  milllion  gallons  of  sewage.  In 
the  Columbus  plant  the  screens  are  raised  by  block  and  chain 
attached  to  an  overhead  trolley.  The  best  diameter  of  mesh  for 
a  given  plant  will  depend  somewhat  upon  the  freshness  of  the 
sewage  and  the  general  nature  of  the  non-fecal  suspended  matter 
carried  by  the  sewage. 

In  some  plants  cage  screens  are  used — rectangular  baskets 
of  rods  or  meshes  into  which  the  sewage  is  discharged,  and  which 
retain  the  screened-out  matters  inside  them,  the  cages  being 
raised  and  emptied  at  intervals.  These  also  are  used  at  Columbus, 
O.,  Gallipolis,  O.,  Saratoga  Springs,  N.  Y.,  and  a  few  other 


402  SEWERAGE. 

places.  The  Gallipolis  cage  is  constructed  of  f-inch  iron  bars 
with  i -inch  clear  opening,  which  is  found  to  be  undesirably  coarse. 
At  Saratoga  f-inch  square  bars,  spaced  f  inch  in  the  clear,  were 
found  best. 

Perhaps  the  most  elaborate  screen  in  this  country  is  that  at 
Reading,  Pa.  This,  called  by  the  inventor  a  "  segregator, "  con- 
sists of  a  cylindrical  screen,  open  at  both  ends,  6  feet  in  diameter 
and  1 6  feet  long,  of  brass  wire  40  meshes  to  the  inch,  which  con- 
tinually revolves  about  a  horizontal  axis  at  the  rate  of  three 
revolutions  per  minute.  The  sewage  passes  through  the  open- 
ings in  the  screen  and  drops  into  a  well  below,  the  suspended 
matter  being  retained  on  the  inside  of  the  screen.  To  clean  the 
screen  a  3-inch  horizontal  pipe  is  suspended  on  each  side  of  the 
screen,  outside  of  and  a  few  inches  from  it,  and  half  way  from 
the  axis  to  the  top.  In  this  pipe  are  holes  at  lo-inch  intervals, 
which  discharge  water,  steam  or  air  against  the  screen,  the  pipe 
meantime  moving  longitudinally  back  and  forth  about  12  inches. 
This  cleaning  is  kept  up  continuously.  Meantime  the  sewage, 
entering  at  one  end,  washes  the  screenings  toward  the  other, 
from  which  they  drop  into  a  bucket  conveyor  which  removes 
them. 

At  Glasgow,  Scotland,  a  screen  of  rod  links,  passing  over 
two  wheels  like  a  link-belt,  and  inclined  45°  with  the  horizontal, 
its  lower  loop  being  in  the  sewage,  removes  the  larger  matters 
and  raises  them  to  an  elevated  platform.  At  Sutton,  England, 
a  revolving  wire  drum  is  used,  something  similar  to  the  Reading 
screen,  geared  to  an  undershot  wheel  which  is  driven  by  the 
sewage. 

Strainers  of  coarse  particles  such  as  coke  or  buckwheat  coal 
have  been  used  but  little  in  this  country.  Coke  and  coal  are  used 
partly  because  of  the  possibility  of  burning  the  organic  matter 
removed  by  the  strainer,  by  using  the  strainer  material  as  fuel 
when  it  is  removed.  Tests  by  the  Massachusetts  State  Board 
showed  that  coke  breeze  (including  pulverized  coke)  in  a  bed 


METHODS    OF    TREATMENT.  403 

12  inches  thick,  gradually  reduced  to  3  inches  by  removing  clogged 
material,  removed  57  per  cent  of  the  bacteria  and  74  per  cent  of 
the  suspended  albuminoid  ammonia.  Screened  coke  removed  72  per 
cent  of  the  bacteria  and  59  per  cent  of  the  suspended  albuminoid 
ammonia.  Fine  bituminous  coal  removed  70  per  cent  of  bacteria 
and  65  per  cent  of  suspended  albuminoid  ammonia.  Buckwheat 
anthracite  (between  J-inch  and  J-inch  mesh)  removed  56  per  cent 
of  bacteria  and  56  per  cent  of  albuminoid  ammonia.  All  were 
operated  at  a  general  rate  of  1,000,000  gallons  per  acre  daily. 
From  the  breeze  bed  were  removed  8  cu.  yds.  of  coke  per  1,000,000 
gallons  of  sewage  strained;  from  the  screened  coke  0.4  cu.yd.;  from 
the  bituminous  coal  0.8  cu.  yd.;  and  from  the  anthracite  0.8  cu.  yd. 
At  Columbus  screened  J-inch  coke  was  used  to  strain  sewage 
at  the  rate  of  1,500,000  to  3,000,000  gallons  per  acre  per  day 
The  results  were  fully  as  good  as  those  just  described,  but  there 
was  considerable  putrefaction  with  objectionable  odor;  and 
5.5  cu.  yds.  of  coke  were  removed  per  1,000,000  gallons  strained. 
They  were  cleaned  at  from  two  to  eight-week  intervals.  Dry- 
ing the  coke  for  burning  required  from  one  to  four  weeks  when 
it  was  spread  upon  land,  and  an  objectionable  odor  was  given 
off.  The  results  obtainable  do  not  seem  to  warrant  the  general 
use  of  this  method,  with  its  objectionable  features;  although 
improvements  in  structure  or  operation  may  be  devised  to  meet 
the  objections. 

ART.  91.    TANK  TREATMENT.    SEDIMENTATION. 

The  general  object  of  tank  treatment  is  clarification.  By 
clarification  is  meant  the  physical  removing  of  matters  in  sus- 
pension, as  is  done  in  the  laboratory  by  the  use  of  filter  paper. 
These  matters  are  of  varying  size  and  consistency,  some  being 
so  fine  as  to  be  microscopic;  and  there  are  matters  known  as 
colloids  which  are  so  minute  as  to  sometimes  render  it  a  matter 
of  debate  whether  they  are  in  solution  or  suspension.  Some 
of  the  matters  are  heavier  than  water,  the  sand  and  other  mineral 


404  SEWERAGE. 

substances  from  the  street  surface  especially;  some  are  lighter 
than  water  and  float  to  the  surface,  such  as  fats,  pieces  of  wood, 
etc.;  and  others  have  a  specific  gravity  of  practically  one  and 
only  gradually  move  either  downward  or  upward.  Some  of  the 
suspended  matters  are  more  or  less  soluble  and  would  be  taken 
into  solution  if  sufficient  time  be  allowed;  in  fact;  the  amounts 
of  matters  in  solution  and  those  in  suspension  in  a  given  sewage 
will  ordinarily  vary  with  the  age  of  the  sewage,  the  former  in- 
creasing and  the  latter  decreasing.  Bacteria  are  in  suspension, 
attached  to  or  embedded  in  particles  of  organic  matter;  so  that 
removal  of  such  matter  by  clarification  or  otherwise  will  at  the 
same  time  remove  large  numbers  of  the  bacteria. 

By  running  sewage  slowly  through  a  tank  or  basin  much 
of  the  suspended  matter  will  settle  out  by  gravity,  forming  a 
sludge  or  thick  liquid  at  the  bottom.  If  run  through  more  rapidly 
only  sand  and  other  coarse  mineral  solids  will  be  deposited. 
When  the  flow  is  slow,  fats,  pieces  of  wood  and  other  light  particles, 
including  organic  matter  which  is  gasifying,  will  float  upon  the 
surface.  The  slower  the  flow  the  larger  the  percentage  of  matter 
which  will  settle  out;  but  this  percentage  increases  much  less 
rapidly  than  the  reduction  in  velocity,  and  such  reduction  becomes 
uneconomical  beyond  a  certain  point. 

The  ordinary  plan  would  be  to  discharge  the  sewage  into 
the  tank  from  a  pipe  at  one  end  and  remove  it  at  the  other  by  a 
pipe  at  the  level  of  the  contained  sewage.  This,  however,  would 
cause  a  current  more  or  less  direct  from  one  pipe  to  the  other, 
giving  too  great  velocity  to  the  flowing  sewage  and  leaving  much 
of  the  tank  contents  practically  stagnant.  This  is  avoided  by 
admitting  the  sewage  through  several  inlets  across  the  end,  or 
better  still  through  an  orifice  or  over  a  weir  extending  entirely 
across  the  end;  the  effluent  being  removed  through  a  similar 
orifice  or  weir  at  the  outlet  end.  If  a  weir  be  used  for  the  latter, 
the  floating  scum  will  pass  off  with  the  effluent.  This  is  generally 
not  desired,  and  the  submerged  orifice  is  therefore  more  common. 


METHODS    OF    TREATMENT.  405 

The  pipe  with  which  the  outlet  orifice  connects  is  brought  up 
to  the  desired  level  of  the  tank  contents,  thus  fixing  this.  The 
form  of  inlet  and  outlet  and  their  approaches  should  be  so  de- 
signed as  to  distribute  the  flow  across  the  entire  width  of  the 
tank  and  also  reduce  the  velocity  of  entrance  as  much  as  possible. 

If  the  sediment  and  scum  remain  long  in  the  tank,  bacterial 
action  begins  and  becomes  more  and  more  active,  especially 
in  the  former.  As  there  is  little  if  any  available  oxygen  in  the  tank 
the  action  is  anaerobic  or  putrefactive.  This  results  in  liquefy- 
ing and  gasifying  much  of  the  organic  matter,  a  large  part  of  the 
remainder  being  finely  comminuted.  As  the  gases  form  they  rise 
to  the  surface,  generally  carrying  organic  matter  with  them, 
sometimes  in  masses  of  several  inches  area.  This  action  and  the 
vertical  currents  set  up  tend  to  prevent  sedimentation  and  also 
carry  into  re-suspension  matter  which  had  already  settled  to  the 
bottom.  Some  part,  also,  of  the  gases  is  probably  taken  into 
solution  in  the  sewage.  The  escaping  gases  may  be  offensive, 
but  generally  are  not  seriously  objectionable  unless  the  tank  be 
very  large  and  the  air  motionless,  and  not  always  then. 

Several  modifications  of  construction  have  been  used  to  meet 
or  avail  of  these  and  other  conditions.  One  aims  to  permit 
sedimentation  and  also  the  gasifying  action  without  any  inter- 
ference of  the  latter  with  the  former.  Another  takes  advantage 
of  the  fact  that  fine  suspended  matter  is  observed  to  adhere  to 
surfaces,  by  introducing  a  great  number  of  surfaces.  These 
will  be  described  later. 

In  such  a  tank  as  is  described  above,  the  sewage  flows  con- 
tinuously, though  slowly,  leaving  at  a  level  only  slightly  lower 
than  that  of  entrance.  This  is  called  a  constant- flow  tank. 
Another  style  of  tank,  called  intermittent- flow,  is  filled  and  allowed 
to  stand  full  for  some  time,  when  the  liquid  is  withdrawn.  This 
requires  the  outlet  pipe  to  be  as  much  below  the  inlet  as  the  fall 
of  sewage  level  when  the  tank  is  emptied,  or  else  that  pumping 
be  resorted  to  for  filling  or  emptying  the  tank.  The  sewage  is 


406  SEWERAGE. 

not  perfectly  quiet  in  most  cases,  but  continues,  with  constantly 
diminishing  velocity,  a  circulating  motion  or  eddying  caused  by 
the  comparatively  rapid  filling.  The  structural  difficulties  and 
details  of  liquid-withdrawing  appliances,  combined  with  the  loss 
of  head,  cause  this  form  of  tank  to  be  but  little  used. 

When  the  velocity  is  so  great  that  only  the  heaviest,  mineral 
matters  are  deposited  it  is  called  a  grit  chamber.  These  are  some- 
times desirable  where  the  combined  system  is  used;  but  in  the 
separate  system  so  little  sand  or  grit  is  carried  that  they  are  con- 
sidered by  experts  to  be  unnecessary.  They  are  generally  objec- 
tionable because  of  the  organic  matter  which  is  apt  to  deposit 
in  them  and  putrefy,  a  velocity  of  even  135  feet  per  hour  being 
insufficient  to  prevent  this  in  Columbus.  Such  grit  as  finds  its 
way  to  a  tank  might  better  settle  with  the  remaining  sludge;  or 
a  bottom  baffle  wall  in  the  tank  near  the  inlet  end  may  serve 
to  collect  the  grit  and  its  accompanying  organic  matter. 

In  a  plain  sedimentation  tank  there  are  to  be  considered, 
besides  the  inlet  and  outlet,  the  length,  width,  depth  and  general 
form.  Except  for  special  forms  to  be  described,  tanks  are  gen- 
erally made  rectangular.  Experiments  at  Columbus  indicated 
that  a  velocity  of  50  feet  per  hour  would  permit  an  amount  of 
precipitation  which  could  be  increased  very  little  by  reducing 
the  rate.  Also  that  prolonging  the  stay  in  the  tank  beyond  4 
hours  did  not  materially  increase  the  deposit.  These  figures 
might  vary  somewhat  with  differences  in  the  nature  of  the  sewage, 
but  agree  almost  exactly  with  the  ideas  of  some  English  authorities. 
Accepting  them,  we  would  have  a  tank  200  feet  long,  and  with 
an  area  of  cross-section  obtained  by  dividing  the  flow  in  cubic 
feet  per  hour  by  50.  In  addition  to  this,  allowance  should  be 
made  for  i  or  2  feet  of  quiescent  sludge  in  the  bottom  of  the  tank. 
From  6  to  8  feet  depth,  allowing  4^  to  6^  feet  for  depth  of  actual 
cross-section  of  moving  sewage,  is  generally  considered  most 
desirable. 

The  width  obtained  by  such  a  calculation  might  be  taken  as 


METHODS   OF    TREATMENT.  407 

that  of  the  tank,  and  in  a  small  plant  probably  would  be.  But 
to  permit  of  putting  a  tank  out  of  service  when  cleaning  without 
intermitting  the  treatment,  several  tanks  may  be  provided;  and 
this  is  also  made  desirable  by  the  tendency  to  the  formation  of 
cross-currents  and  other  causes  of  non-uniform  flow  in  a  wide 
tank.  Several  tanks  placed  side  by  side  are  therefore  desirable 
if  the  volume  of  flow  exceeds  say  1,000,000  gallons  a  day. 

Such  a  tank  will  remove  from  40  to  60  per  cent  of  the  sus- 
pended organic  matter,  and  a  higher  per  cent  of  suspended  in- 
organic matter.  The  sludge  must  be  removed  at  intervals  of 
3  to  6  days  in  summer  and  2  to  4  weeks  in  winter,  if  active  putre- 
faction is  to  be  avoided.  The  sludge  deposited  will  be  80  to  95 
per  cent  water,  and  disposing  of  it  presents  serious  difficulties 
in  many  cases.  This  will  be  considered  in  another  article.  While 
large  numbers  of  bacteria  are  removed  by  sedimentation,  the 
number  leaving  in  the  effluent  is  still  so  large  that  subsequent 
treatment  to  remove  them  is  necessary  if  bacterial  purification 
is  considered. 

The  removal  of  the  sludge  may  be  facilitated  by  special  con- 
struction or  apparatus,  the  simplest  of  which  is  the  sloping  of 
the  bottom  of  each  tank  toward  a  central  gutter,  which  itself 
slopes  toward  an  outlet  at  one  end  or  in  the  middle.  This  out- 
let may  lead  by  a  pipe  to  a  sludge  pit  or  sludge  bed.  The  super- 
natant liquid  may  be  drawn  off  with  the  sludge,  may  be  pumped 
to  an  adjacent  tank,  or  may  remain  in  the  tank  after  the  sludge 
has  flowed  out.  A  scraper,  of  the  nature  of  a  squeegee,  is  some- 
times used  to  force  the  sludge  to  the  outlet,  but  this  is  generally 
unnecessary.  In  intermittent-flow  tanks  the  effluent  is  generally 
drawn  off  by  a  hinged  pipe,  its  free  end  being  maintained,  by  a 
float,  about  3  to  6  inches  below  the  surface,  the  lower  end  being 
connected  to  an  outlet  pipe.  When  the  effluent  begins  to  run 
cloudy  the  remaining  contents  of  the  tank,  or  sludge,  is  drawn 
off  into  a  sludge  well. 

Sedimentation  tanks  should  be  practically  water-tight  to  pre- 


408  SEWERAGE 

vent  pollution  of  the  soil  and  undermining  of  the  foundation. 
They  should  have  a  hard  and  smooth  surface  to  facilitate  removal 
of  sludge.  Steel  plates  might  be  used  to  meet  these  requirements 
but  would  be  unnecessarily  expensive  and  subject  to  rapid  dete- 
rioration by  rust.  Brick  or  concrete  is  ordinarily  employed,  the 
latter  being  more  common  at  the  present  time.  The  interior 
of  a  concrete  tank  should  ordinarily  be  floated  down  to  a  smooth 
sidewalk  finish.  Brick  work  should  be  smooth,  with  the  joints 
pointed.  Enameled  brick  are  sometimes  used  because  adhering 
matter  can  so  easily  be  removed  from  them.  The  tanks  are 
underground  in  the  majority  of  cases,  since  the  surface  of  sewage 
in  them  is  practically  at  the  level  of  the  flow  line  of  the  sewer, 
except  when  it  is  necessary  to  pump  the  sewage. 

Sedimentation  tanks  are  sometimes  roofed  over,  in  other  cases 
they  are  left  uncovered.  Roofing  is  somewhat  expensive,  espe- 
cially where  the  tank  is  large.  It  offers  the  advantage  of  pro- 
tecting the  tank  from  winds,  which  would  create  eddies  and  cur- 
rents in  a  large  tank,  which  would  interfere  with  sedimentation; 
they  maintain  a  more  uniform  temperature,  preventing  the  surface 
of  the  sewage  from  freezing  (although  this  is  likely  to  occur  only 
in  very  cold  climates) ;  and  conceal  the  tanks  from  view  and 
prevent  the  diffusion  of  odors,  thus  palliating  imaginary  or  real 
offenses  to  sight  and  smell.  For  small  tanks  an  ordinary  frame 
roof,  with  the  gables  closed  in,  will  ordinarily  serve  the  purpose, 
although  a  more  durable  and  ornamental  structure  may  be  ob- 
tained by  the  use  of  masonry  and  a  slate  roof.  For  larger  tanks 
a  more  common  construction  is  a  concrete  or  brick  roof  of  groined 
arches  supported  by  masonry  pillars  resting  at  regular  intervals 
upon  the  floor  of  the  tank.  If,  as  is  desirable,  a  large  tank  is 
divided  by  longitudinal  walls  into  a  series  of  narrow  tanks,  pillars 
are  unnecessary  and  either  frame  or  arched  masonry  roofs  may  be 
supported  on  the  partition  walls.  Given  the  dimensions  calcu- 
lated as  indicated  above,  the  remainder  of  the  design  and  con- 
struction of  a  sedimentation  tank  would  be  similar  to  that  of  any 


METHODS    OF     TREATMENT. 


409 


like  structure  for  coi.taining  water;   except  for  the  special  inlet 
and  outlet  constructions,  as  already  described. 

On  account  of  popular  prejudice,  as  well  as  to  reduce  the  cost 
of  the  considerable  area  occupied  by  horizontal  tanks,  they  will 
generally  be  placed  as  far  as  possible  from  built-up  sections. 


FIG.  37. — ELEVATION  AND  SECTION  OF  DORTMUND  RECEIVING  AND  PRECIPI- 
TATING TANKS  AT  CHICAGO  WORLD'S  FAIR. 

Where  this  cannot  be  done  the  area  required  can  be  reduced  by 
use  of  a  vertical  tank. 

In  the  vertical  tank  the  sewage  flows  upward  and  the 
precipitant  collects  on  the  bottom,  which  is,  in  the  "Dort- 
mund" tank,  conical  in  shape.  Fig.  37  shows  the  Chicago 
vertical-flow  tanks,  modelled  after  those  at  Dortmund.  If 
the  sludge-pipe  is  made  to  discharge  ij  to  2  feet  below  the 
level  of  the  sewage  in  the  tank,  this  head  will  be  sufficient  to 
force  it  out  without  pumping,  providing  it  contains  90%  to 


410  SEWERAGE. 


of  water,  as  most  sludge  does.  In  this  tank,  however, 
some  sludge  is  likely  to  adhere  to  the  sides  of  the  cone,  which 
must  be  cleaned  occasionally  by  hand  or  by  a  revolving 
scraper.  In  the  Candy  tank*  the  bottom  is  flat  and  the  sides 
circular  and  vertical;  and  both  sides  and  bottom  are  cleaned 
by  a  squeegee  revolving  on  a  central  vertical  shaft,  the  sludge 
being  forced  into  and  through  a  pipe  at  the  bottom  by  a 
hydrostatic  head  of  18  inches  as  just  described.  In  the 
upward-flow  tanks  the  sewage  rises  at  the  rate  of  .005  to  .01 
foot  per  second;  and  as  the  precipitant  falls  at  an  average 
rate  of  .02  to  .03  foot  per  second,  it  slowly  reaches  the  bottom 
^>f  the  tank.  Experience  seems  to  show,  however,  that  not 
quite  so  large  a  percentage  of  organic  matter  is  removed  in  these 
as  in  horizontal-flow  tanks.  Upward-flow  tanks  are  particularly 
adapted  to  localities  where  the  available  space  is  small. 

0 

ART.  92.    TANK  TREATMENT.    PRECIPITATION. 

To  hasten  the  sedimentation  and  render  it  more  thorough, 
as  well  as  to  remove  a  part  of  the  matters  in  solution,  chemi- 
cals are  in  many  instances  added  to  the  sewage.  It  was  at  first 
thought  that  by  chemical  treatment  a  large  part  of  the  organic 
matter  in  solution  could  be  rendered  insoluble  and  precipitated, 
and  Slater  cites  over  450  patents  granted  in  England  for  chemicals 
to  be  so  used.  It  is  now  generally  recognized,  however,  that 
practically  only  the  solids  in  suspension  and  5  %  to  1  5  %  of  those 
in  solution  can  be  removed  by  this  method.  As  only  about  one- 
fifth  of  the  total  solids  are  in  suspension,  it  is  evident  that  but  a 
small  percentage  of  them  is  removed,  although  these  may  include 
half  of  the  organic  matter. 

Precipitation  is  largely  or  entirely  a  physical  process.  When 
lime,  for  instance,  is  added  to  sewage  it  unites  with  the  carbonic 

*See  Engineering  News,  December  28,  1899. 


OF    THE 

UNIVERSITY 


METHODS   OF    TREATMENT.  411 

acids  to  form  carbonate  of  lime,  and  with  sulphuric  acid,  if  any 
be  present,  to  form  sulphate  of  lime  or  gypsum;  both  of  which 
are  insoluble  in  water  and  settle  to  the  bottom  of  the  tank,  entangling 
and  carrying  down  with  them  flocculent  matters  in  suspension. 
If  a  large  amount  of  lime  be  used,  calcium  hydrate  instead  of 
carbonate  is  formed,  clarifying  the  sewage.  Sufficient  lime 
generally  remains  in  solution  in  the  carbonic  and  other  acids  to 
render  the  sewage  alkaline.  If  iron  sulphate  or  aluminum  sul- 
phate be  added  to  sewage  thus  made  alkaline,  a  flocculent  pre- 
cipitant of  hydrate  of  iron  or  hydrate  of  aluminum  is  formed 
which  seems  to  precipitate  slightly  more  of  the  soluble  matter 
than  does  lime.  Ferrous  sulphate  seems  to  be  useless  without 
the  addition  of  lime  to  combine  with  the  excess  of  carbonic  acid 
and  with  the  sulphuric  acid  of  the  ferrous  sulphate.  Ferric  sul- 
phate is  more  readily  precipitated  and  more  completely  insoluble 
than  the  ferrous  salt,  and  the  use  of  lime  with  it  is  not  so  necessary; 
as  is  also  the  case  with  aluminum  sulphate  or  crude  alum,  ordinary 
sewage  containing  enough  alkali  to  decompose  these  salts.  It  is 
found  that  if  more  lime  is  used  than  will  combine  with  the  carbonic 
acid  in  the  sewage,  no  benefits  result  from  the  additional  lime; 
and  the  free  lime  is  objectionable  because  of  the  danger  that  it 
will  kill  fish  in  the  water  reached  by  the  effluent,  and  that  it  will 
cause  a  secondary  precipitation  in  the  effluent  or  stream  which 
receives  it.  With  ferric  and  alum  salts,  however,  the  precipi- 
tation increases  with  the  amount  used,  though  at  a  less  rate  after 
a  certain  point  is  reached.  Some  sewage,  such  as  that  of  Worcester, 
Mass.,  contains  so  much  ferric  sulphate  that  it  is  useless  to  add 
more. 

Of  the  great  number  of  materials  (not  necessarily  "chemicals" 
in  the  popular  use  of  the  word)  proposed,  only  a  few  have  been 
found  practicable,  many  being  too  expensive.  Lime,  ferrous 
and  ferric  sulphate  and  sulphate  of  alumina  are  believed  to  be 
the  only  ones  used  in  this  country.  A  few  patented  preparations 
are  used  in  England.  From  tests  made  by  the  Massachusetts 


412 


SEWERAGE. 


State  Board  of  Health  certain  conclusions  were  reached   as  to 
relative  effectiveness  and  cost,  which  are  given  in  Table  No.  27. 

TABLE  No.  27. 

RESULTS    OF    PRECIPITATION    OF    SEWAGE    WITH    VARIOUS    CHEMICALS. 
From  Laboratory  Experiments  of  the  Mass.  State  Board  of  Health. 


Precipitant. 

Pounds  per  Million 
Gallons. 

Per  Cent.  Removed. 

Cost  of 
Chem- 
icals. 

A. 

B. 

Loss  on 
Ignition. 

Albumi- 
noid 
Ammonia. 

Bacteria. 

Plain  sedimentation 

23 

35 

38 

49 
48 
26 

2 
21 
26 

33 
47 
43 
47 
56 
45 
37 
55 
49 
52 
44 
39 
64 
60 
71 
29 
40 
61 
42 

47 
62 

58 

24 
43 
44 
56 
56 

21 

18 

37 
4i 

20 
50 
65 
56 

61 
59 
38 
5i 
56 
66 

3i 
47 
68 

67 
78 
48 
64 

67 
60 
61 

70 
70 

19 
67 
78 
93 

98 
IO 

Lime  

800 

1200 

i6oot 

2OOO 

$2.40 
3.60 
4.80 
6.00 
2-15 
4-3° 
2.60 

3-6i 

3-35 
4-25 
5-75 
8.15 
6.70 
11.90 

2-75 
3.60 
4.80 
5-5«> 
3-95 
5-!5 
7.00 
8.50 
11.50 
6.80 

IO.2O 
13.60 

8.00 
9.20 
15.10 
16.60 

Copperas  

500 

IOOO 
200 
4OO 
500 
500 
500 
500 
IOOO 
200O 
500 
650 
870 
IOOO 

500 
500 

IOOO 
IOOO 
2OOO 

500 
750 

IOOO 

500 
500 

IOOO 
IOOO 

Copperas     (A)    and 
lime  (B)      .    . 

58ot 
63oJ 
400 
7°°J 

I2OO 
2000 

Soot 

IIOOJ 

95 
98 
34 
95 
99+ 
99+ 
98 

99+ 
97 
86 

91 
91 
74 
91 
95 
99 
99+ 
86 

91 
97 
78 
90 
96 
96 

Sulphate  alumina  .... 

Sulphate  alumina  (A) 
and  lime  (B)  

Ferric  sulphate 

400 

800 

500 

IOOO 
IOOO 

Ferric  sulphate    (A)  j 
and  lime  (B)  .  .  .  ] 
I 

400 

800 

500 

IOOO 

t  Amount  adjusted  to  CO2  in  sewage. 


Amount  adjusted  to  copperas. 


In  each  case  the  time  allowed  for  sedimentation  was  one  hour. 
The  calculations  of  cost  were  based  upon  the  following  unit  costs  in 
the  year  1908:  Lime  (70%  available  CaO),  $6  per  ton.  Copperas, 


METHODS   OF    TREATMENT.  413 

(55%  available  FeSOJ,  $10  per  ton.  (Sugar  sulphate  of  iron, 
containing  64%  available  FeSO4,  can  be  used,  reducing  the  cost 
about  15%).  Crude  alum  (58%  available  A12(SO4)3),  $20  per 
ton.  Ferric  sulphate,  $27  per  ton. 

Besides  the  substances  above  referred  to  a  few  others  give  good 
results,  but  the  majority  of  precipitants  bearing  other  names  are 
but  combinations  of  these  with  other  more  or  less  beneficial  sub 
stances.     Some  of  the  best  known  of  these  are: 

The  ABC  process,  using  alum,  blood,  clay,  and  seven  other 
materials,  alum  and  clay  constituting  about  97%  of  the  mixture. 

Alumino-ferric  process,  using  crude  alum,  with  a  trace  of 
iron  salts. 

Ferrozone,  composed  of  crude  alum,  ferrous  sulphate  with 
magnetic  oxide,  and  a  few  other  mineral  matters. 

A  comparison  of  all  available  data  would  indicate  that  under 
the  most  intelligent  and  careful  supervision  chemical  treatment 
will  in  actual  practice  remove  85%  to  95%  of  the  suspended 
organic  matter,  and  10%  to  15%  of  that  in  solution;  or  80%  to 
93%  of  the  total  suspended  matter,  and  50%  to  60%  of  all 
organic  matter. 

The  amount  and  kind  of  chemical  which  is  most  effective 
for  any  given  case  will  depend  upon  the  strength  and  character 
of  the  sewage.  This  may  already  contain  a  large  amount  of  iron 
or  lime,  or  it  may  be  very  acid  and  require  more  than  the  ordinary 
dose  of  an  alkali.  The  amount  of  lime  should  be  sufficient  to 
make  the  sewage  slightly  alkaline,  as  indicated  by  litmus  or 
phenolphthalein.  Commercial  lime  will  yield  65%  to  80%  of  its 
weight  in  calcium  oxide;  and  this  should  be  at  least  equal  in 
quantity  to  the  carbonic  acid  in  the  sewage.  The  addition  of 
more  than  this  will  increase  the  efficiency  of  the  treatment  very 
little  and  will  give  an  alkaline  effluent  which  is  injurious  to  fish; 
also  the  additional  lime  will  slowly  precipitate  out,  leaving  a  deposit 
on  the  banks  and  bottom  of  the  stream;  and  if  the  effluent  is 
highly  alkaline,  it  will  not  readily  nitrify  in  subsequent  filtration. 


414  SEWERAGE. 

At  Worcester,  Mass.,  where  analyses  are  taken  every  half- 
hour  and  great  care  is  used  in  apportioning  the  chemicals  in 
accordance  with  the  chemical  composition  of  the  sewage,  there 
was  used  in  1905  an  average  of  i  pound  per  1,000  gallons,  the 
sewage  being  very  acid.  At  several  intervals  of  ij  to  2  hours' 
duration  each,  during  every  week-day,  the  sewage  contains  more 
than  enough  copperas  to  act  as  a  precipitant,  and  this  is  retained 
and  mixed  with  later  sewage  which  does  not  contain  much 
iron. 

For  various  manufacturing  wastes  it  is  often  necessary  to 
use  special  chemicals.  From  a  series  of  experiments  continued 
through  several  years  the  Massachusetts  State  Board  of  Health 
finds  that  all  such  wastes  can  be  purified,  but  that  there  are 
practical  difficulties  in  filtering  certain  of  these  without  previous 
treatment.  Thus,  wool  waste-liquors  should  be  treated  with 
sulphuric  acid  or  calcium  chloride  or  other  chemical  for  cutting 
the  fats,  lime  and  copperas  having  small  effect  on  them;  and 
should  be  greatly  diluted  if  to  be  nitrified.  Mechanical  methods 
such  as  skimming  and  applying  centrifugal  force  have  been  used 
for  fats  with  some  success.  Tannery  liquors  can  be  freed  of  60% 
or  more  of  their  organic  constituents  by  the  use  of  lime,  and  can 
then  be  filtered.  The  presence  of  arsenic,  as  from  tanneries  or 
paper-works,  of  sulpho-naphthol,  as  from  tanneries,  or  of  any 
other  germicide,  will  interfere  with  nitrification  unless  they 
be  removed  or  formed  into  insoluble  compounds  by  use  of 
chemicals. 

Besides  the  directly  chemical  processes  there  are  a  few  which 
might  be  called  Indirect-Chemical.  Those  best  known  use 
electricity  for  manufacturing  the  precipitating  chemicals  from  the 
sewage  itself,  from  electrodes,  or  from  salt  water.  The  chemicals 
thus  appear  in  the  sewage  in  their  nascent  state,  in  which  con- 
dition they  are  considered  to  be  most  active. 

In  England  in  1894  there  were  174  precipitation  plants,  among 
60  of  which  20  used  lime  alone,  n  used  ferrous  sulphate  (commonly 


METHODS   OF    TREATMENT.  415 

called  copperas),  8  used  lime,  copperas,  and  sulphate  of  alumina, 
and  9  used  "ferrozone."  In  this  country  there  are  at  present 
precipitation  plants  at  Worcester,  Mass.,  Providence,  R.  L, 
New  Rochelle  and  White  Plains,  N.  Y.,  Canton,  Alliance,  Glenville 
and  Oberlin,  O.,  Anaconda,  Mont.,  and  possibly  one  or  two 
smaller  ones.  Lime  is  used  at  all  these,  in  combination  with 
copperas  in  most  of  them.  The  first  chemical  precipitation  plant 
in  the  United  States,  that  at  East  Orange,  N.  J.,  was  abandoned 
a  number  of  years  ago  in  favor  of  discharge  into  the  Passaic  River. 

The  chemicals  added  in  most  American  plants  amount  to 
30  per  cent  or  more  of  the  total  sludge;  which  additional  matter 
requires  to  be  disposed  of.  The  sludge  is  denser  than  that  from 
precipitation  only,  and  more  easily  compressed  (see  Article  100). 
At  Worcester,  in  1905,  the  average  amount  of  sludge  formed  was 
3,420  pounds  per  million  gallons  of  sewage,  the  lime  used  averag- 
ing 999  pounds.  At  Canton,  O.,  in  1907  the  sludge  averaged 
about  520  pounds  of  sewage  matter  per  million  gallons,  and  the 
lime  applied,  2,000  pounds,  the  poor  precipitation  results  being 
largely  due  to  too  great  velocity  in  the  settling  tank.  "The 
results  at  Canton  and  Alliance  have  shown  the  well-known  solvent 
action  of  lime  on  suspended  organic  matter,  with  the  result  that 
the  effluent  from  a  chemical  precipitation  plant  is  oftentimes 
stronger  organically  and  hence  more  offensive  than  is  the  crude 
sewage  after  the  removal  of  the  suspended  matters  by  plain 
sedimentation  alone.  The  result  of  lime  treatment  at  both 
Canton  and  Alliance  is,  of  course,  merely  a  rough  clarification 
and  the  production  of  a  sewage  effluent  which  is  ill  smelling 
and  such  as  to  cause  a  decided  nuisance."  (Report  of  Ohio 
State  Board  of  Health  for  1908).  At  Worcester  also  it  is  found 
that  sludge  from  chemical  precipitation  decomposes  with  the 
evolution  of  gas  much  like  septic  sludge. 

When  a  flocculent  precipitant  is  formed  and  sufficient  time 
is  allowed  for  the  precipitation  of  it  (8  hours  in  some  cases)  the 
effluent  is  freed  from  much  of  the  very  fine  suspended  matter 


416  SEWERAGE. 

which  clogs  filters  and  which  is  not  ordinarily  removed  by  plain 
sedimentation.  Also,  with  careful  management  the  total  amount 
of  suspended  organic  matter  removed  is  considerably  increased 
by  chemical  treatment.  At  Worcester  about  93  per  cent  of  the 
suspended  and  12  per  cent  of  the  dissolved  albuminoid  ammonia 
is  removed.  This  and  Providence,  however,  are  the  only 
plants  in  this  country  which  are  producing  really  satisfactory 
results.  This  is  partly  because  their  sewage  is  acid;  but  chiefly 
because  of  the  careful  and  intelligent  management,  which  a  small 
plant  does  not  often  receive.  At  Worcester  samples  of  sewage 
are  taken  every  half  hour,  the  quantity  of  each  being  as  nearly 
as  possible  in  proportion  to  the  amount  of  sewage  being  received 
at  the  time  of  sampling.  Effluent  samples  are  taken  hourly. 
It  would  seem  that  for  a  small  plant  plain  sedimentation  is 
generally  preferable  to  precipitation. 

In  the  chemical  precipitation  of  sewage  we  must  prepare  the 
chemicals,  introduce  them  into  the  sewage,  permit  the  latter  to 
deposit  the  insoluble  matter,  draw  off  the  effluent,  and  dispose 
cf  this  and  of  the  deposit  or  sludge. 

The  chemicals  are  ordinarily  obtained  as  crystals  or  in 
powdered  form.  As  such  they  would  not  readily  or  quickly 
mix  with  the  sewage,  and  they  are  usually  dissolved,  better 
in  sewage  than  in  water,  to  form  a  more  or  less  saturated 
solution,  in  which  form  they  are  introduced  into  the  sewage. 
In  Glasgow  the  lime-mixer  consists  of  a  cast-iron  box,  through 
which  passes  a  vertical  shaft  driven  by  belting,  to  the  shaft 
being  attached  four  horizontal  radial  bars  at  different  eleva- 
tions and  of  different  lengths.  Pieces  of  chain  are  used  as 
agitators  which  drag  along  the  bottom  to  prevent  deposit. 
A  horizontal  grating  with  7  X  i^-inch  spaces  fills  the  interior 
at  2  feet  8  inches  from  the  top,  through  which  grating  the 
lime  must  percolate.  The  depth  of  water  in  the  mixers  is 
usually  3  feet  3  inches.  The  alum  is  mixed  in  four  wooden 
vats  3X5X10  feet,  the  agitation  being  effected  by  exhaust 


METHODS    OF    TREATMENT.  417 

air  from  the  sludge-lifts  which  is  led  into  the  bottoms  of  the 
vats. 

In  East  Orange  the  mixers  were  in  the  form  of  cylindrical 
cast-iron  vats  4  feet  in  diameter,  with  conical  bottoms,  each 
overlaid  with  a  perforated  plate.  The  chemicals  were  placed 
on  the  plates  and  air  blown  in  from  the  bottom  as  in  the 
Glasgow  plant. 

At  Worcester  the  mixing-tanks  are  8  X  16  X  8J  feet 
deep,  of  iron  in  brick  masonry.  Two  and  one-half  tons  of 
lime  can  be  mixed  at  a  time  in  each.  Compressed  air  is  used 
here  also  as  an  agitator. 

The  concentrated  solution  thus  prepared  is  admitted  to 
the  sewage  and  should  be  thoroughly  mixed  with  it.  This 
should  be  done  before  the  sewage  is  pumped,  if  pumping  is 
necessary;  both  because  this  assists  in  the  mixing,  and 
because  less  suspended  matter  in  the  sewage  has  been  taken 
into  solution,  in  which  form  but  little  of  it  can  be  removed 
by  chemicals.  To  obtain  thorough  mixing  with  the  sewage 
it  is  better  to  maintain  a  continuous  flow  of  precipitant  than 
to  introduce  a  certain  amount  at  intervals  of  one  to  fifteen 
minutes;  although  the  latter  is  generally  the  simpler  plan. 
The  amount  of  chemical  introduced  per  minute  should  be 
proportioned  to  the  amount  of  sewage  flowing  and  to  its 
chemical  composition.  For  this  purpose  analyses  should  be 
taken  about  once  an  hour;  and  the  flow  at  any  moment 
should  be  ascertainable  by  observing  a  weir  inserted  in  the 
sewage  channel,  or  otherwise.  A  gate  or  cock  can  be  pro- 
vided with  an  index  or  gauge  by  which  the  amount  of  chem- 
ical required  from  time  to  time  can  be  caused  to  flow  into  the 
sewage.  In  very  small  plants,  however,  it  may  be  found 
cheaper  to  introduce  the  chemical  at  such  a  fixed  rate  during 
the  day,  and  such  another  during  the  night,  as  has  been  found 
to  produce  the  desired  purification  with  the  highest  rate  of 
jlow  of  the  strongest  sewage;  thus  avoiding  the  expense  of 


41 8  SEWERAGE. 

keeping  a  chemist  constantly  on  the  work.  To  effect  the 
mixing  of  the  chemical  and  the  sewage,  the  former  is  generally 
introduced  while  the  latter  is  flowing  along  an  open  channel, 
which  is  provided  lower  down  with  baffle-boards  forming  a 
"  salmon-ladder,"  or  with  a  small  under-shot  wheel. 

From  this  channel — after  being  pumped,  if  this  is  neces- 
sary— the  sewage  flows  to  settling  tanks  in  which  the  insoluble 
matter  precipitates.  These  tanks  are  in  general  like  those  for 
plain  sedimentation.  Those  at  Worcester  are  i66§  feet  long. 
At  Canton  4  tanks,  each  50X96  feet,  receive  the  sewage  in  series, 
but  most  of  the  sludge  collects  in  the  first. 

The  cost  of  the  Canton  plant,  adapted  for  2,000,000  gallons 
a  day,  was  $31,545,  including  $5,000  for  land.  The  cost  of 
operation  is  about  $3100  to  $3800  a  year,  of  which  $2000  is  for 
salaries  of  three  engineers.  This  is  about  14  to  16  cents  per  per- 
son tributary  to  the  sewers.  The  Glasgow  plant,  to  treat  10,- 
000,000  gallons  daily,  cost  $335,000  exclusive  of  site.  The  cost 
of  the  treatment  in  $17  per  million  gallons,  or  14^  cents  per  capita 
annually.  London,  to  handle  250,000,000  gallons  daily,  paid 
$4,066,448  for  a  plant,  including  $662,322  for  six  sludge-ships. 
The  precipitation  expenses  are  $2.98  per  1,000,000  gallons,  sludge 
disposal  $1.66.  The  New  Rochelle  plant,  to  treat  750,000  gallons 
daily,  cost  about  $19,000.  The  East  Orange,  for  1,500,000  gallons 
daily,  cost  $75,000;  maintenance  60  cents  per  capita  annually, 
exclusive  of  interest;  lime  95  cents  per  barrel,  alum  ij  cents  per 
pound.  Round  Lake  in  1892  paid  3^  cents  per  pound  for  per- 
chloride  of  iron.  The  White  Plains  plant,  for  400,000  gallons 
daily,  cost  $50,049;  maintenance  $12  per  day  for  250,000  gallons. 
AtChautauqua  the  cost  of  the  plant  was  $16,500;  that  of  chemicals 
(lime  at  83.2  cents  per  barrel  and  alum  at  2.15  cents  per  pound) 
was,  in  1893,  .04  cent  per  capita  per  day;  total  maintenance  57 
cents  per  capita  per  year.  At  the  Columbian  Exposition  $8.80 
per  ton  was  paid  for  lime,  $13.40  for  copperas,  and  $20.40  for  alum. 


METHODS  OF    TREATMENT.  419 


ART.  93.    TANK  TREATMENT.    SEPTIC  TANKS. 

The  fact  that  sludge  in  the  bottom  of  a  sedimentation  tank 
will  in  time  begin  to  putrefy  and  give  off  gases  has  been  referred 
to;  also  that  this  action  interferes  somewhat  with  sedimentation. 
Study  of  putrefactive  action,  however,  showed  that  by  it  much 
of  the  organic  matter  in  sewage  is  liquefied  or  gasified;  and  it 
had  been  learned  that  liquefaction  precedes  oxidation  in  the  reduc- 
tion of  organic  matter.  Owing  largely  to  the  study  of  the  subject 
by  Donald  Cameron,  of  Exeter,  England,  there  was  developed 
a  method  of  utilizing  this  putrefactive  or  septic  action  in  tanks. 
Cameron  believed  the  tanks  must  be  covered  to  exclude  light  and 
air,  because  the  septic  action  was  performed  by  anaerobic  bacteria. 
To  such  tanks  he  gave  the  name  septic  tanks. 

"The  essential  difference  between  settling  tanks  and  septic 
tanks  is  that  the  solid  matters  deposited  in  the  former  are  removed 
at  frequent  intervals  and  otherwise  disposed  of,  while  with  the 
latter  the  sludge  is  allowed  to  remain  for  longer  periods  in  the 
tank,  where  it  is  subjected  to  hydrolytic  or  bacteriolytic  action.  By 
these  means  a  portion  of  the  organic  matter  is  converted  into 
unoffensive  gases  or  into  soluble  compounds  which  pass  off  with 
the  outflowing  sewage.  When  septic  tanks  first  came  into  use 
it  was  stated  by  many  that  all  of  the  sludge  would  be  destroyed 
ultimately,  and  that  mechanical  handling  of  the  sludge  would 
be  necessary  but  rarely.  That  this  view  was  largely  erroneous 
has  been  proved  by  experience,  but  it  is  still  a  fact  that  a  very 
considerable  portion  of  the  deposited  matter  may  be  destroyed. 
Ultimately,  however,  the  space  occupied  by  the  deposit  increases 
to  such  an  extent  that,  if  the  quantity  of  sewage  for  which  the  tank 
was  designed  is  passed  through  daily,  the  rate  of  flow  becomes  so 
great  that  the  sedimentation  of  suspended  matter  is  greatly  im- 
paired, and  under  such  a  condition  it  is  necessary  to  remove  the 
sludge  mechanically.  But  as  sludge  destruction  is  dependent 


420  SEWERAGE. 

on  slow  bacterial  action,  and  as  that  action  may  not  become 
operative  immediately,  it  is  essential,  to  get  the  best  results,  that 
septic  tanks  be  cleaned  only  when  absolutely  necessary."  (Report 
of  Mass.  State  Board  of  Health  for  1908). 

Reference  has  also  been  made  to  floating  matter  in  sedimenta- 
tion tanks.  The  action  of  the  gases  in  a  septic  tank  increase  the 
amount  of  this  scum,  and  under  favorable  conditions  (which  are 
not  thoroughly  understood)  this  coheres  into  a  continuous  cover- 
ing which  becomes  dense  and  leathery  and  several  inches  in  thick- 
ness. Little  septic  action,  or  bacterial  action  of  any  kind,  takes 
place  in  the  scum.  In  many  tanks  no  scum  at  all  forms,  but  its 
absence  does  not  seem  to  interfere  with  the  action  of  the  tank. 
The  scum  is  in  many  cases  the  home  of  great  quantities  of  maggots, 
earthworms  and  similar  low  forms  of  animal  life,  and  also  gives 
growth  to  plant  life  of  various  kinds.  It  may  become  a  foot  or 
more  thick  and  undesirably  contract  the  free  flow  area  of  the  tank. 
This  has  been  avoided  in  Birmingham,  Ala.,  by  flooding  sewage 
over  the  scum  and  breaking  this  up,  when  much  of  it  will  settle 
to  the  bottom  and  be  added  to  the  sludge.  Some  amount  of  scum 
is  perhaps  desirable,  however,  to  protect  the  sewage  from  temper- 
ature changes  and  agitation  by  winds,  which  interfere  with  sed- 
imentation and  septic  action. 

In  the  sludge  anaerobic  bacteria  gradually  develop,  and  liquefy 
and  gasify  the  organic  matter.  A  space  of  from  two  weeks  to 
several  months  is  required  for  the  full  development  of  septic 
action  in  the  sludge;  this  time  being  required  for  the  requisite 
number  of  bacteria  to  multiply.  If  the  sewage  is  fresh  and  not 
well  broken  up  and  commingled,  the  time  required  is  generally 
longer  than  if  it  be  stale.  Some  classes  of  organic  matter  are 
easily  decomposed,  others  resist  decomposition  for  months;  but 
in  time  a  point  is  reached  where  the  volume  of  sludge  remains 
nearly  constant,  the  additions  balancing  the  amount  leaving  as 
liquid,  gas  and  finely  comminuted  matter.  But  even  then  there 
is  some  matter  which  decomposes  so  slowly  (if  at  all)  that  it  is 


METHODS   OF    TREATMENT.  421 

not  practicable  to  retain  it  until  it  decomposes;  but  this  matter 
is  removed  at  intervals  of  from  once  in  six  months  to  once  in  six 
years.  No  method  has  been  devised  of  removing  this  resistant 
matter  without  removing  the  remaining  sludge  also;  and  the  tank 
is  emptied  and  the  process  begun  anew,  some  of  the  fresher  sludge 
being  sometimes  left  in  the  tank  to  "seed"  it. 

The  effluent  from  a  septic  tank  generally  has  a  more  objec- 
tionable appearance  than  the  crude  sewage,  being  dark  and  turbid. 
But  it  really  contains  less  suspended  matter  by  25  to  50  per  cent, 
most  of  which  is  in  solution  but  some  of  which  has  disappeared 
as  gas.  The  suspended  matter  left  is  more  finely  divided.  The 
bacterial  content  is  sometimes  reduced,  but  at  other  times  (gen- 
erally in  warm  weather)  the  number  is  increased.  The  sludge 
from  a  septic  tank  is  less  offensive  than  that  from  a  sedimentation 
tank,  is  more  thoroughly  worked  over  and  dries  out  more  readily. 

Tests  made  by  the  Massachusetts  State  Board  of  Health  gave 
the  composition  of  dry  septic  sludge  as  follows:  Mineral  matter, 
45  to  71  per  cent;  total  organic  matter,  29  to  54  per  cent;  organic 
nitrogen,  i.i  to  2.9  per  cent;  fats,  8.8  to  11.9  per  cent;  carbon, 
25.1  to  29.8  per  cent. 

The  gas  from  septic  tanks  has  as  its  principal  ingredients 
methane,  carbon  dioxide  and  nitrogen,  the  proportions  varying  . 
widely  with  different  tanks.  Sulphuretted  hydrogen  and  other 
hydrogen  gases  are  sometimes  present.  The  quantities  given 
off  vary  widely,  measurements  showing  from  1.5  to  7  or  8  cu.  ft. 
of  gas  per  100  cu.  ft.  of  sewage.  The  amount  apparently  depends 
more  upon  the  temperature  and  putrescibility  of  the  sludge  than 
upon  the  amount  of  organic  matter  present.  The  gas  is  highly 
inflammable,  and  suggestions  have  been  made  that  it  might  be  used' 
for  illumination  or  gas  engines.  But  its  variableness  as  to  volume 
and  composition  are  apparently  insuperable  obstacles  to  this. 

The  sewage  should  not  stay  too  long  in  a  septic  tank,  from 
6  to  12  hours  being  found  best — the  latter  for  fresh  sewage.  t  Longer 
than  this  increases  little,  if  any,  the  amount  of  sedimentation, 


422  SEWERAGE. 

and  may  result  in  undesirable  action  upon  the  matter  in  solution. 
The  true  function  of  the  septic  tank  is  to  remove  and  hydrolyze 
the  suspended  matter.  It  was  once  believed  that  the  effluent 
contained  gases  and  products  of  anaerobic  activity  which  would 
inhibit  later  oxidation ;  but  this  is  not  now  believed  to  be  the  case. 
Consequently  aeration  of  septic  effluents,  which  was  formerly 
more  or  less  common,  is  unnecessary;  and  as  it  involves  loss  of 
head,  and  the  creation  of  a  nuisance  by  odors,  it  is  undesirable. 
There  may  also  be  "  a  needless  loss  of  temperature  which  may 
seriously  interfere  with  the  finishing  devices  during  winter  weather. 
Odors  have  not  been  especially  pronounced  near  septic  tanks; 
and,  at  distances  greater  than  from  100  to  200  feet,  in  none  of 
the  plants  studied  has  there  been  any  cause  for  criticism  in  this 
regard."  (Report  of  Ohio  State  Board  of  Health  for  1908.) 
The  effluent  from  many  of  the  Ohio  tanks  contains  dissolved 
oxygen,  this  reaching  as  high  as  50  or  60  per  cent  of  complete 
saturation  at  times;  although  generally  it  did  not  exceed  one-half 
to  one-fourth  of  the  amount  found  in  the  crude  sewage. 

The  septic  tank  removes  in  some  cases  more,  in  some  less, 
suspended  matter  than  does  a  sedimentation  tank.  But  the  matter 
removed  is  in  general  that  which  putrefies  readily  and  that  which 
resists  reduction.  The  effluent  of  the  septic  tank  is  therefore 
in  better  condition  for  disposal  by  dilution  than  merely  settled 
effluent.  Moreover  the  grosser  matters  which  cause  surface 
clogging  of  filters  are  removed.  It  is  a  question,  however,  whether 
septic  effluent  is  better  adapted  for  disposal  on  fine-grain  filters, 
as  the  fineness  of  the  suspended  matter  and  absence  of  the  surface 
mat  which  is  formed  on  a  filter  when  coarser  matters  are  present 
result  in  a  deeper  penetration  of  the  deposits. 

A  septic  tank,  being  essentially  a  sedimentation  tank,  is  con- 
structed in  much  the  same  way.  Its  cubical  contents  should 
be  that  of  from  6  to  12  hours  flow  of  sewage.  If  larger,  the 
effluent  may  be  subject  to  undesirable  anaerobic  action,  and  it 
has  been  found  also  that  the  amount  of  sludge  which  resists  re- 


METHODS    OF    TREATMENT.  423 

duction  is  increased.  As  the  volume  of  sewage  flow  varies  from 
day  to  day,  and  generally  increases  continually,  as  the  population 
increases,  2  or  more  tanks  should  be  provided,  and  provision 
made  for  adding  others  as  needed.  With  this,  arrangements 
should  be  made  by  which,  when  the  flow  through  the  tank  or  tanks 
in  service  becomes  greater  than  desired,  another  shall  come  into 
service;  and  when  the  flow  diminishes  one  shall  be  put  out  of 
service.  In  perhaps  the  majority  of  plants,  especially  of  small 
ones,  this  flexibility  is  not  provided,  but  only  one  tank  is  used; 
but  the  results  from  many  of  those  are  far  from  satisfactory. 

Efforts  have  been  made  in  some  plants  to  minimize  the  taking 
of  sludge  into  resuspension.  At  Worcester  two  low  baffle  walls 
divide  the  bottom  of  the  tank  into  three  equal  parts,  and  above 
these  'are  suspended  baffles  or  scum  boards,  submerged  a  few 
inches.  These  tend  to  confine  the  most  vigorous  action  to  the 
first  third  of  the  tank  and  permit  resedimentation  in  the  last  third. 

A  recent  form  of  construction  for  effecting  this  is  the  Emscher 
tank.  (So  named  because  of  its  originating  in  the  Emscher 
district,  Germany). 

The  Emscher  tank  is  made  deeper  than  the  ordinary  sedimenta- 
tion tank,  or  from  20  to  30  feet  deep.  Across  the  top  of  the  tank 
are  inclined  floors  which  practically  form  a  V-trough  or  troughs 
for  almost  the  full  width  of  the  tank,  these  floors,  however,  not 
quite  coming  together  at  the  bottom  and  one  extending  a  short 
distance  beyond  the  bottom  of  the  other.  If  the  tank  be  of  any 
size  there  may  be  two  or  more  of  these  troughs  placed  side  by 
side.  The  sewage  flows  through  the  troughs  and  the  sediment, 
settling  to  the  bottom,  slides  through  the  opening  into  the  tank 
beneath.  Practically  all  of  the  motion  of  translation  takes  place 
in  the  trough  and  consequently  there  is  no  disturbance  in  the  tank 
beneath  except  that  occasioned  by  the  settling  down  of  the  sludge 
and  ebullition  of  gas.  On  the  other  hand,  as  the  sludge  in  the 
bottom  of  the  tank  gradually  develops  septic  action  and  the  gases 
therefrom  rise  through  the  sewage,  they  cannot  enter  the  troughs 


424 


SEWERAGE. 


METHODS    OF    TREATMENT.  425 

and  thus  interfere  with  sedimentation,  because  of  the  overlapping 
of  one  floor  beyond  the  other;  but  the  gases  rise  outside  of  the 
troughs  to  a  small  area  along  the  edges  of  the  tank,  where  they 
escape. 

In  order  to  utilize  to  full  advantage  the  entire  length  of  the 
tank,  or  both  tanks  when  there  is  more  than  one,  Mr.  Imhof,  the 
inventor,  recommends  reversing  the  flow  every  few  days  or  weeks; 
since  it  is  found  that,  as  in  other  tanks,  the  largest  collection  of 
sludge  forms  near  the  inlet.  The  sludge  from  these  tanks  is 
withdrawn  from  time  to  time  if  it  should  become  necessary.  It 
is  seen  that  the  volume  of  the  tank  must  be  very  much  larger  than 
for  an  ordinary  tank  if  the  same  velocity  of  flowing  sewage  is 
to  be  obtained,  since  this  actually  occupies  but  a  small  part  of 
the  total  area.  The  necessity  for  such  deep  tanks,  20  feet  or 
more,  is  not  apparent,  since  the  only  use  of  that  portion  below  the 
troughs  is  for  the  storing  of  sludge.  It  is  stated  that  the  effluent 
from  these  tanks  is  much  more  readily  oxidized  by  finishing  filters 
than  that  from  the  ordinary  septic  tank;  probably  because  of 
the  freedom  from  gas  and  especially  from  the  fine  matters  thrown 
up  into  resuspension  by  the  gas  in  an  ordinary  septic  tank. 

Another  variation  of  tank  treatment  is  that  devised  by  Mr. 
Travis  of  England,  known  as  the  Hydrolytic  tank.  In  this  the 
aim  is  similar  to  that  of  the  Emscher  tank — the  separation  of 
the  sludge  from  the  flowing  sewage;  but  in  addition  the  principle 
of  surface  adhesion  of  colloids  is  taken  advantage  of  for  removing 
these  fine  matters  from  the  sewage.  The  tank,  which  has  the 
form  of  a  flat  V  at  the  bottom,  is  divided  into  three  compartments 
by  a  longitudinal  arch-shaped  wall  enclosing  a  lower  compartment, 
on  top  of  which  is  a  vertical  double  wall  enclosing  a  narrow  channel 
and  dividing  the  upper  portion  into  two  compartments.  The 
arch  has  openings  along  the  line  of  its  junction  with  the  V-shaped 
bottom,  and  also  in  its  crown.  The  outlet  end  of  the  tank  has 
a  level  weir  which  is  divided  by  the  arch  so  as  to  apportion  a  definite 
width  of  weir  to  each  of  the  compartments.  The  compartment 


426  SEWERAGE. 

under  the  arch  receives  the  sludge  through  the  openings  in  the  arch, 
the  sedimentation  occurring  in  the  other  two  compartments.  Sewage 
enters  the  upper  or  sedimentation  chambers  only,  the  other  com- 
partment receiving  sewage  and  sludge  from  them.  There  is, 
however,  some  flow  through  this  bottom  compartment  and  over 
the  weir  at  the  end,  the  amount  being  determined,  as  before 
stated,  by  the  relative  length  of  the  weir  at  the  end  of  this  com- 
partment. At  Hampton,  England,  this  section  of  the  weir  is 
20  per  cent  of  the  total  length.  It  is  believed  that  tank  and  weir 
proportions  which  will  cause  the  sewage  to  remain  4  hours  in 
the  sedimentation  chambers  and  12  hours  in  the  sludge  or  reduc- 
tion chamber  give  the  best  results.  In  this  tarik,  as  in  the  other, 
the  gases  formed  in  the  sludge  compartment  will  not  reach  the 
sedimentation  chambers  to  interfere  with  the  sedimentation. 
In  this  tank,  however,  there  is  some  flow  through  the  sludge  tank; 
probably  because  this  was  thought  necessary  to  maintain  maximum 
septic  action.  In  addition  to  this  construction,  the  sedimenta- 
tion chambers,  except  in  the  first  one-fourth  of  their  length,  con- 
tain a  number  of  vertical  or  practically  vertical  surfaces  or  curtain 
walls,  oh  which  the  colloids  collect  by  surface  adhesion,  to  slide 
off  in  patches  as  the  accumulation  becomes  sufficiently  dense 
and  weighty  to  detach  itself  from  the  surfaces.  The  V-shaped 
bottom  of  the  sludge  tank  facilitates  withdrawing  of  sludge 
through  a  pipe  placed  at  the  angle  of  the  V. 

Both  of  these  tanks  are,  it  is  seen,  more  complicated  and  more 
expensive  than  the  ordinary  septic  tank,  and  it  may  be  questioned 
whether  the  results  obtained,  even  were  they  as  excellent  as  is 
claimed  by  the  inventors,  make  the  additional  expense  worth 
while,  unless  under  exceptional  conditions.  The  general  idea, 
however,  seems  to  possess  much  merit  and  probably  less  ex- 
pensive modifications -of  it  could  be  used  to  advantage  in  many 
cases. 


METHODS   OF    TREATMENT. 


427 


The  largest  septic  tank  plant  in  the  country  is  that  at  Columbus, 
O.,  where  provision  is  made  for  treating  20,000,000  gals,  a  day,  by 
four  tanks  56^X150  ft.,  and  two  tanks  115^X262  ft.,  each  about 
12  feet  deep,  uncovered.  The  tanks  are  divided  into  three  sec- 
tions by  transverse  walls.  These  tanks,  of  concrete  throughout, 


FIG.  39. — INTERIOR  OF  CHAMPAIGN,  ILL.,  COVERED  SEPTIC  TANK. 
(From  Engineering  AVzt'-s.) 


cost  $48,070  for  masonry,  $3,640  for  earth  work,  $12,530  for  sluice 
gates,  and  $2,490  for  other  details;  or  about  $3,336  per  million 
gals. 

A  tank  at  Lake  Forest,  111.,  capacity  200,000  gals,  per  day 
cost  $8,000.  One  at  Delaware,  O.,  of  100,000  gals,  capacity 
cost,  including  coke  filters,  $12,000.  One  at  Lakewood,  O., 
300,000  gals,  capacity,  cost,  including  625  acres  of  contact  filters, 
$24,175.  One  at  Mansfield,  O.,  1,000,000  gals,  capacity,  with 
ij  acres  of  contact  filters,  cost  $65,547.  One  at  Wauwatosaj 
Wis.,  handling  100,000  gals,  a  day,  cost  $5,370.  Previous  to  the 


>8 


SEWERAGE. 


completion  of  the  Columbus  plant  the  one  at  Birmingham,  Ala., 
was  probably  the  largest  septic  tank  plant  in  the  country,  com- 


FIG.  40. — INTAKE   OF   SEPTIC  TANKS,   BIRMINGHAM,   ALA.     SHOWS   SCUM, 
WITH   WEEDS   GROWING  IN  IT.  • 


FIG.  41. — DISCHARGE-WEIRS,  SEPTIC  TANKS,  BIRMINGHAM,  ALA. 
(From  Municipal  Journal  and  Engineer.) 

prising  six  tanks  each  100  X  20  feet  by  10  feet  deep,  treating  about 
5,000,000  gals,  a  day. 


METHODS    OF    TREATMENT.  429 


ART.  94.    OXIDATION. 

Sedimentation  and  precipitation,  as  described,  remove  40 
to  60  per  cent  of  the  organic  impurities,  but  leave  most  of  those 
in  solution  unchanged,  the  effluent  of  the  septic  tank  even  con- 
taining a  greater  amount  of  soluble  organic  matter  than  the  original 
sewage.  Moreover  the  matter  removed  forms  a  considerable 
amount  of  sludge  which  must  be  disposed  of  in  some  way.  For 
both  reasons  they  can  be  considered  but  preliminary  processes 
in  treatment.  Final  disposal  of  the  sludge  is  imperative,  and 
there  are  few  cases  where  the  effluent  also  does  not  require  further 
treatment.  A  change  of  the  putrescible  matter  of  either  into 
permanently  non-putrescible,  harmless  compounds  or  elements 
can  be  attained  only  by  changing  it  into  mineral  forms  by  oxida- 
tion. When  complete  oxidation  has  taken  place  the  carbon  has 
taken  the  form  of  carbonic  acid  and  the  nitrogen  the  form  of 
nitric  acid,  both  probably  combining  at  once  with  some  mineral 
base  in  the  sewage.  While  this  change  is  described  in  chemical 
terms,  it  has  been  found  that  no  mere  mixing  of  chemicals  with 
sewage  will  produce  it,  but  it  is  in  part  a  biological  process. 

This  complete  process  is  a  true  purification  of  sewage.  The 
organic  matter  may,  however,  be  partially  purified,  or  "modified," 
and  left  in  such  condition  that  it  will  not  readily  putrefy,  but  can 
be  discharged  into  a  stream  or  onto  land  with  no  more  danger  of 
giving  offense  than  if  composed  of  so  much  leaves  or  straw;  the 
amount  approximating  500  to  1,000  pounds  per  million  gallons. 

Stated  briefly,  investigation  to  date  seems  to  prove  the 
following  as  facts  :  Lifeless  organic  matter  is  stable  in  the  ab- 
sence of  moisture,  but  in  its  presence  a  large  proportion  of 
such  matter  is  readily  broken  down  in  structure  and  is  resolved 
into  minerals,  appearing  generally  as  mineral  compounds. 
Albuminous  matter  is  particularly  unstable;  while  woody 
fibre,  bones,  and  similar  matters  are  quite  stable,  and  cause 


43°  SEWERAGE. 

most  of  the  difficulty  experienced  in  sewage  purificaticn. 
Organic  matter  is  decomposed  not  so  much  by  chemical  action 
as  by  certain  classes  of  bacteria,  some  of  which  exist  in  all 
soils,  and  probably  in  water  and  air  as  well.  Certain  of  these 
seem  to  require  the  presence  of  free  oxygen  for  their  action  if 
not  for  their  life,  and  are  called  aerobic  ;  others,  the  anaerobic, 
live  and  work  best  in  the  absence  of  light  and  air ;  and  still 
others  are  facultative,  i.e.,  can  live  and  act  under  either  con- 
dition. 

When  sewage  enters  a  sewer  it  generally  contains  a  small 
amount  of  free  oxygen  and  a  few  nitrates.  By  the  action  of 
aerobic  bacteria  the  free  oxygen  is  taken  up  by  the  urea,  am- 
monia, and  easily  decomposable  matter  present,  and  nitrateS 
are  formed.  At  the  same  time  anaerobic  or  facultative  bac- 
teria, together  with  a  few  aerobic  ones,  are  at  work  breaking 
down  the  albuminous  matters  into  soluble  nitrogenous  com- 
pounds; which  operation  is  carried  on  with  increased  activity 
after  the  disappearance  of  all  free  oxygen,  the  anaerobic  bac- 
teria being  the  more  effective  in  liquefying  sewage.  It  is  dur- 
ing this  stage, — in  some  cases  at  its  beginning,  in  others  when 
it  is  well  advanced, — that  the  sewage  is  generally  received  at 
the  purification  works  or  discharged  into  the  river  or  ocean. 

If  it  should  now  be  left  stagnant,  as  in  a  cesspool  or  septic  tank, 
the  anaerobic  bacteria  would  continue  the  breaking  down  of  the 
organic  matters,  even  the  cellulose  and  fibrous  matter  being 
finally  liquefied.  During  this  anaerobic  action  much  of  the 
organic  matter  is  changed  into  hydrogen  gases  (since  no  free 
oxygen  is  present),  such  as  marsh-gas,  and  sulphuretted  hydro- 
gen, and  nitrogen,  much  of  which  escapes  into  the  air;  the  sewage 
meantime  becoming  offensive  to  sight  and  smell.  In  this  con- 
dition it  is  called  septic  sewage.  Liquefaction,  either  septic  or 
aerobic,  must  generally  precede  oxidation. 

If  oxygen  be  admitted  to  the  sewage  as  soon  as  it  becomes 
well  liquefied,  oxidation  will  quickly  begin,  and  the  dissolved  and 


METHODS   OF   TREATMENT. 


431 


finely  comminuted  organic  matter  will  be  changed  to  innocuous 
and  inoffensive  nitrates  and  carbonates. 

Previous  to  oxidation  most  of  the  decomposed  nitrogenous 
matter  which  has  not  escaped  as  gas  has  taken  the  form  of 
ammonia.  By  oxidation  and  the  action  of  the  aerobic  bac- 
teria the  ammonia  becomes  changed  largely  into  nitric  of 
nitrous  compounds  with  some  base,  such  as  potassium  of 
sodium,  present  in  the  sewage.  Probably  none  of  these 
changes  is  the  effect  of  only  one  class  of  bacteria,  but  several 
classes  work  both  together  and  successively.  These  processes 
are  summarized  by  Dr.  Rideal  as  shown  in  the  following 
table : 


Substances  dealt  with. 


Characteristic  Products. 


INITIAL. 

Transient    aerobic 
changes   by  the   oxygen  e  a 
of  the  water-supply,  rap- 
idly passing  to  : 

FIRST  STAGE. 
Anaerobic       liquefac- 
tion and  preparation  by 
hydrolysis. 

SECOND  STAGE. 
Semi-anaerobic  break- 
ing  down   of  the   inter- 
mediate   dissolved  bod- 
ies. 

THIRD  STAGE. 
Complete  aeration  ; 
nitrification. 


Urea,    ammonia,    and 
sily      decomposable 
matters. 


Albuminous  matters. 
Cellulose  and  fibre. 
Fats. 


A  m  i  d  o  -  c  ompounds. 
Fatty  acids.  Dissolved 
residues.  Phenolic 
bodies. 


Soluble  nitrogenous 
compounds.  Fatty  acids. 
Phenol  derivatives. 
Gases.  Ammonia. 


Ammonia. 
Gases, 


Nitrites. 


Ammonia  and    carbo- 
naceous residues. 


Carbonic  acid,  water, 
and  nitrate. 


The  process  above  outlined  is,  so  far  as  we  know,  the  only 
one  other  than  burning  (rapid  oxidation)  by  which  organic 
matter  can  be  permanently  deprived  of  its  noxious  properties. 

It  is  important  to  note  that  liquefaction  must  precede  bacterial 
nitrification,  and  that  the  anerobes  are  the  most  effective  liquefy- 


43 2  SEWERAGE. 

ing  agents;  also  that  any  attempt  to  reverse  the  order  of  these 
processes  will  merely  retard  final  purification. 

One  of  the  difficulties  of  stimulating  these  processes  in  the 
purification  of  sewage  is  that  the  various  components  of  this 
resist  liquefaction  so  unequally  that  it  seems  impossible  to 
make  the  conditions  at  all  times  most  favorable  to  each  of  the 
contained  organic  matters.  If  light  and  air  are  excluded  to 
encourage  the  anaerobic  action  until  all  the  fats  and  fibres  are 
liquefied,  the  albumens  will  meantime  reach  the  last  stages  of 
offensive  putrefaction.  By  making  the  conditions  alternately 
favorable  to  aerobic  and  anaerobic  action  at  short  intervals, 
each  particle  of  matter  may  be  oxidized  as  soon  as  it  has  be- 
come prepared  for  this  action  and  objectionable  odors  be 
largely  avoided ;  but  under  these  conditions  neither  class  of 
bacteria  will  develop  and  act  to  the  best  advantage. 

The  bacteria  necessary  for  the  above  process  exist  in  the 
sewage,  but  their  numbers  and  the  celerity  of  their  action  can 
be  greatly  increased  by  collecting  and  retaining  them  in  a 
permanent  lodging-place  with  favorable  environment  and  sup- 
plying a  constant  amount  of  pabulum  in  successive  doses  or 
in  a  continuous  stream  of  sewage.  Most  plans  for  the  de- 
struction of  sewage  have  for  their  aim  the  supplying  of  these 
conditions.  In  some  but  one  lodging-place  is  afforded,  and 
either  both  the  liquefying  and  nitrifying  organisms  exist  and 
act  side  by  side  (possibly  only  aerobic  liquefiers  acting)  or  in 
separate  parts  of  the  plant,  or  no  liquefaction  takes  place  after 
the  sewage  enters  the  plant.  Other  plants  are  divided  into 
two  or  three,  or  even  more,  separate  parts,  each  devoted  to  a 
•different  class  of  bacteria.  In  many  instances  sewage  is  flowed 
over  and  settles  down  through  porous  soil,  in  passing  through 
the  interstices  of  which  it  comes  into  intimate  contact  with 
the  contained  air  and  with  the  bacteria  which  adhere  to  the 
soil  particles ;  and  if  the  passage  of  the  sewage  be  sufficiently 


METHODS   OF    TREATMENT.  433 

slow  and  the  number  of  nitrifying  bacteria  sufficiently  large, 
the  oxldizable  liquefied  organic  matter  will  all  be  transformed 
into  nitrates.  If  the  number  of  bacteria  is  not  originally 
sufficient,  they  will  increase  with  great  rapidity;  and  if  a  con- 
stant amount  of  sewage  be  applied  continually  to  a  given  plot 
of  ground,  and  sufficient  oxygen  be  furnished,  the  number  of 
bacteria  will  in  a  few  days  become  sufficient  to  effect  complete 
nitrification.  If  the  sewage  be  simply  turned  continuously 
upon  tliis  land,  the  interstitial  air  will  soon  yield  up  all  its 
oxygen,  and  nitrification  will  cease.  But  if  the  land  be  allowed 
to  drain  out,  the  interstices  will  again  fill  with  air  and  the 
operation  can  be  repeated ;  and  this  can  go  on  indefinitely,  or 
until  the  filter  becomes  clogged  with  unliquefied  matter.  This 
is  the  principle  upon  which  purification  by  land  and  by  filter- 
beds  acts.  If  the  land  be  too  open  and  porous,  the  sewage 
will  pass  through  too  rapidly  to  permit  of  thorough  bacterial 
action.  If  it  be  composed  of  too  fine  grains,  capillary  attrac- 
tion will  be  so  great  that  it  will  drain  out  and  be  reaerated 
but  slowly.  The  time  required  for  draining  out  a  bed  is  in 
some  plants  reduced  by  making  the  bed  very  porous  and 
holding  the  sewage  in  it  during  fixed  periods  of  time  by  clos- 
ing the  outlet.  In  other  cases  the  beds  are  not  drained  out 
at  all,  but  air  is  continuously  forced  in  under  a  few  ounces 
pressure.  In  still  others  the  sewage  is  sprinkled  over  a  very 
porous  bed  and  trickles  through,  at  no  time  filling  the  pores  and 
driving  out  the  air. 

These  methods,  depending  upon  the  aerobic  bacteria  only, 
must  use  sewage  in  which  are  no  matters  in  suspension  not  easily 
liquefied  by  aerobes,  or  else  be  subject  to  clogging,  the  fine-grain 
filters  mainly  upon  the  surface,  the  coarse-grain  ones  in  all  their 
interstices.  For  this  reason  some  preliminary  process  for  remov- 
ing or  liquefying  the  suspended  matter  must  generally  be 
provided.  Sedimentation,  chemical  precipitation  and  septic 
action  are  those  most  commonly  used;  and  these  tank  treat- 


434  SEWERAGE. 

ments  are  therefore  essentially  preliminary  ones,  to  be  followed 
by  others. 


ART.  95.    INTERMITTENT  FILTRATION  AND  IRRIGATION. 

In  sewage  and  water  purification  the  word  " filter"  is  generally 
applied  to  a  collection  of  particles  of  any  size,  through  which  the 
liquid  is  passed.  The  individual  particles  may  be  as  fine  as  the 
finest  sand  or  as  large  as  cobble  stones.  Evidently  straining  out 
impurities  can  be  no  part  of  the  function  of  the  latter;  and  the 
straining  effect  of  the  fine  sand  filter  is  considered  but 
incidental. 

In  any  filter  "the  essential  conditions  are  very  slow  motion 
of  very  thin  films  of  liquid  over  the  surface  of  the  particles  that 
have  spaces  between  them  sufficient  to  allow  air  to  be  in  contact 
with  the  films  of  liquid.  With  these  conditions  it  is  essential 
that  certain  bacteria  be  present  to  aid  in  the  process  of  nitrifica- 
tion." (Mass.  State  Board  of  Health,  1890).  During  this  slow 
motion  in  contact  with  air  and  in  the  presence  of  aerobic  bacteria, 
the  dissolved  organic  matter  is  largely  oxidized.  The  colloids 
and  fine  suspended  matters  which  have  not  been  previously  re- 
moved adhere  to  the  surfaces  of  the  filter  particles  or  grains,  where 
they  are  retained  and  worked  over  more  slowly,  probably  being 
liquefied  by  aerobic  or  facultative  bacteria.  Nitrogenous  matters 
have  been  found  to  be  retained  in  a  filter  for  several  years  before 
final  oxidation.  The  percentage  of  suspended  matter  so  retained 
depends  partly  upon  the  slowness  of  flow  through  the  filter,  partly 
upon  the  area  of  surfaces  offered  for  adhesion;  and  this  last 
increases  with  the  fineness  of  the  particles. 

The  requisite  number  of  bacteria  will  develop  in  the  filter 
if  favorable  conditions  be  offered,  but  this  will  require  some  days, 
and  meantime  the  oxidation  effected  will  be  less  than  the  maximum 
efficiency  of  the  plant.  The  establishing  of  these  most  favorable 
conditions  involves  the  application  at  constant  rates  of  a  sewage 


METHODS   OF   TREATMENT.  435 

of  uniform  character,  and  the  continuous  presence  of  oxygen,  or 
frequent  renewals  of  the  supply;  and  fairly  high  temperature  is 
helpful. 

Theoretically  the  results  from  using  filters  of  differing  sizes 
of  grains  should  differ  in  degree  rather  than  in  kind;  but  it  is 
found  that  the  effluents  obtained  are  quite  different  in  their  nature ; 
a  partial  reason  for  which  may  lie  in  the  different  methods  of  opera- 
tion made  necessary  by  the  different  structures.  The  general 
classes  of  filters  in  common  use  are  fine-grain  (sand),  contact, 
and  sprinkling  or  trickling.  Slate  beds,  wave  beds  and  one  or 
two  others  also  are  used,  the  principles  of  which  differ  somewhat 
from  those  just  outlined. 

As  explained,  the  organic  matters  are  oxidized  to  nitrates, 
which  compounds  are  assimilated  by  plant  life  of  all  grades.  In 
some  cases  vegetation  is  grown  directly  on  the  filters,  when  the 
treatment  is  called  "broad  irrigation."  Natural  soil  is  almost 
invariably  used  for  this  purpose.  Filters  proper  may  be  built 
of  sand,  gravel  or  broken  stone,  or  may  simply  utilize  natural 
soil  when  this  is  suitable. 

"  Broad  irrigation  means  the  distribution  of  sewage  over 
a  large  surface  of  ordinary  agricultural  ground,  having  in  view 
a  maximum  growth  of  vegetation  (consistently  with  due 
purification)  for  the  amount  of  sewage  supplied.  Filtration 
means  the  concentration  of  sewage  at  short  intervals,  on  an 
area  of  specially  chosen  porous  ground,  as  small  as  will  absorb 
and  clean  it,  not  excluding  vegetation,  but  making  the  produce 
of  secondary  importance."  (Royal  Commissioners  on  Metro- 
politan Sewage  Discharge.)  No  more  definite  line  could  be 
drawn  between  irrigation  and  filtration  than  is  indicated  by 
these  definitions.  In  many  plants  the  same  land  is  used 
alternately  for  both  methods.  The  nitrates  which  would  pass 
off  with  the  effluent  in  filtration  are  to  a  certain  extent 
to  20$  probably)  absorbed  by  vegetation. 


4*6  SEWERAGE. 

In  broad  irrigation  much  of  the  sewage  must  at  times  be 
diverted  from  the  crops — as  in  rainy  weather  or  after  the 
fruit  has  matured.  If  this  is  not  done,  the  crops  cannot  be 
raised  to  advantage.  In  some  locations  it  will  not  be  seri- 
ously objectionable  to  turn  the  sewage  at  these  times  into  the 
streams,  particularly  in  rainy  weather  when  these  will  be  in 
flood;  but  where  this  is  not  permissible  provision  must  be 
made  to  treat  the  sewage  otherwise,  as  on  filtration-beds. 
If  this  plan  is  adopted  sewage  should  be  turned  upon  the 
filtration-beds  two  or  three  times  a  week  to  keep  alive  in 
them  the  nitrifying  bacteria. 

Irrigation-fields  are  ordinarily  odorless,  but  on  close, 
humid  days  in  summer  the  moist  deposit  on  the  surface  gives 
off  an  appreciable  dish-water  smell,  which,  however,  is  seldom 
noticeable  more  than  100  yards  from  the  field.  The  intensity 
of  the  odor  seems  to  increase  not  directly  with  but  as  the 
square  or  some  higher  power  of  the  area  irrigated.  It  is  not 
advisable  to  place  such  grounds  in  the  midst  of  a  settled 
community,  but  a  quarter  of  a  mile  should  be  sufficient  inter- 
vening space. 

Sewage  is  used  in  irrigation  much  as  water  is,  except  that 
it  should  not  come  into  direct  contact  with  berries,  celery, 
cabbage,  or  the  edible  portions  of  any  plant.  In  some  cases, 
generally  where  grass  of  some  kind  is  grown,  the  sewage  flows 
slowly  all  over  the  land  in  a  thin  layer.  Where  corn  or 
vegetables  are  grown  they  are  usually  planted  on  the  narrow 
ridges  between  ploughed  furrows  into  which  the  sewage  flows, 
and  where  it  stands,  soaking  downward  and  sideways  into  the 
soil.  The  roots  of  vegetation  and  the  vegetable  mould  which 
forms  on  the  surface  of  the  ground  prevent  the  rapid  absorp- 
tion of  the  sewage,  and  unless  the  subsurface  soil  be  clayey 
or  quite  non-porous,  sub-drains  are  not  often  necessary,  but 
ditches  are  carried  through  the  farm  at  intervals  to  receive 
the  drainage.  If  the  sewage  is  not  clarified  before  being 


METHODS    OF    TREATMENT.  437 

applied  to  the  soil,  an  impervious  skin  shortly  forms,  composed 
of  filaments  of  paper,  rags,  and  similar  matters,  together  with 
grease  and  the  more  stable  organic  matter;  and  this  must  be 
frequently  removed  if  the  ground  is  to  be  re-aerated  and  kept 
absorptive.  This  matter,  which  has  little  odor,  can  be  piled 
in  a  dry  spot  and  burned  occasionally. 

If  the  ground  is  not  level,  the  furrows  should  follow  con- 
tours, that  the  sewage  may  stand  in  them.  If,  on  a  sloping 
land,  furrows  are  not  desired,  the  catchment  system  may  be 
employed.  In  this  a  series  of  ridges  following  the  contours 
are  placed  at  intervals  of  15  to  100  feet  down  the  slope;  the 
sewage  is  held  behind  each  ridge  until  it  overflows  it,  when 
the  surplus  runs  over  the  surface  until  intercepted  by  the 
next  ridge.  The  object  of  the  ridges  is  to  prevent  the  sewage 
from  gathering  into  channels  and  attaining  erosive  velocity. 
Hence  the  steeper  the  land  the  closer  should  be  the  ridges  to 
each  other.  This  method  was  adopted  at  Wayne,  Pa.,  on 
a  steep  rocky  hill  100  feet  high  with  a  soil  of  micaceous 
loam. 

The  ridge-and-furrow  system  is  particularly  applicable  to 
level  land.  In  this  system  the  ground  is  divided  into  beds 
sloping  from  a  central  ridge  to  gutters  or  furrows  on  each  side, 
each  furrow  being  common  to  two  adjacent  beds.  Another 
furrow  for  distributing  the  sewage  runs  along  each  ridge,  from 
each  side  of  which  the  sewage  overflows  in  a  thin  sheet.  The 
beds  are  generally  15  to  20  feet  from  each  ridge  to  either 
furrow,  and  of  any  convenient  length.  The  slope  of  the  beds 
is  a  matter  of  judgment,  being  steeper  the  more  porous  the 
soil  in  order  that  the  sewage  may  be  evenly  distributed. 

Sewage  is  in  some  cases  distributed  through  main  carriers 
of  iron  or  of  vitrified  pipes,  under  pressure  produced  either 
by  gravity  or  by  pump,  to  hydrants,  as  at  Pulman,  111.; 


438  SEWERAGE. 

through  vitrified  pipes  by  gravity;  or  through  open  channels, 
lined  with  concrete  or  with  split  pipe;  and  in  many  recent  works 
the  channels  are  used  without  any  lining  whatever.  From  the 
main  -carriers  the  sewage  is  diverted  by  means  of  simple  gates 
to  secondary  carriers,  which  are  often  but  ploughed  furrows,, 
the  location  of  which  is  changed  when  they  become  clogged  with 
sewage.  These  furrows  should  be  closer  together  the  more  per- 
vious the  soil,  to  effect  uniform  distribution.  If  the  subsoil  is 
clayey,  or  the  water-table  is  near  the  surface,  it  may  be  necessary  to 
lay  sub-drains.  These  are  generally  placed  under  the  ridges  if 
the  ridge-and-furrow  method  is  used.  From  3  to  6  feet  is 
the  customary  depth,  depending  upon  the  porosity  of  the  soil 
and  the  crops  grown.  Sub-drains  cannot  be  used  near  osiers, 
since  these  root  deep  and  stop  up  the  drains. 

Open,  porous  soils  are  best  adapted  to  irrigation ;  although 
they  should  not  absorb  the  sewage  faster  than  25,000  to- 
30,000  gallons  per  acre  per  day  to  obtain  good  results  from 
crops.  But  if  the  crops  are  only  an  incident  ("  intermittent 
filtration  "),  the  more  porous  the  soil  the  better.  Clay  land 
may  be  improved  for  irrigation  by  ploughing-under  ashes  or 
sand,  but  can  never  be  made  as  desirable  as  naturally  porous 
soil.  The  sewage  from  50  to  150  or  200  persons  can  be  used 
for  irrigating  one  acre,  depending  upon  the  quality  of  the 
soil.  At  the  Paris  sewage  farm  at  Acheres  11,766  gallons 
per  acre  daily  is  fixed  as  the  limit,  but  this  is  largely  street- 
water.  At  Berlin  the  population  contributing  to  each  acre 
of  the  irrigation-fields  is  156. 

Crops  of  all  kinds  have  been  grown  on  sewagi  farms. 
Italian  rye-grass  seems  particularly  well  adapted  to  this 
purpose,  absorbing  sewage  indefinitely  and  growing  so  closely 
as  to  choke  out  weeds,  but  is  not  very  hardy  in  this  country 
north  of  Washington,  D.  C.  It  is  grown  in  flat  beds.  It 


METHODS    OF   TREATMENT.  439 

makes  excellent  fodder  and  is  a  good  crop  for  dairy  farms,* 
but  when  cut  can  be  kept  only  by  ensilage.  It  is  sown  at  the 
rate  of  45  to  50  pounds  per  acre. 

In  the  northern  United  States  corn  has  given  excellent 
satisfaction.  At  South  Framingham,  Mass.,  100  bushels  of 
shelled  corn  per  acre  has  been  grown;  at  Brockton,  Mass.,  70 
bushels  is  obtained.  The  corn  is  grown  in  hills  3  feet  apart, 
the  ridges  being  about  4  feet  apart,  and  is  irrigated  through 
the  furrows. 

Wheat  has  been  grown  at  the  Salt  Lake  City  farm,  36 
bushels  per  acre,  and  barley  28  bushels  per  acre;  but  cereals 
are  apt  to  develop  stalk  rather  than  grain  on  sewage  farms. 
Walnuts  give  good  results  in  Pasadena,  Cal.  Cabbages, 
parsnips,  carrots,  potatoes,  rhubarb,  turnips,  cauliflower, 
celery,  onions,  squashes,  beans,  peas,  asparagus,  as  well  as 
other  garden  truck,  and  tobacco,  have  all  been  grown  on  sew- 
age farms,  as  have  timothy,  alfalfa,  and  other  grasses.  Only 
actual  trial  in  a  given  section  of  country  will  determine  the 
crop  which  there  grows  best  and  finds  the  best  market. 

Meadow-land  at  Paris  (Gennevilliers)  is  uninjured  by  a 
flow  of  50,000  gallons  per  acre  per  day.  Lucerne  grass  takes 
36,000  gallons  ;  artichokes  12,000  gallons  ;  flowers  and 
parsley  11,000;  leeks,  cabbage,  and  celery  7000;  beets, 
carrots,  and  beans  4000;  potatoes,  asparagus,  and  peas  3000 
gallons  per  acre  per  day. 

A  city  of  100,000  inhabitants,  if  treating  its  sewage  by 
irrigation,  would  require  500  to  2000  acres  of  suitable  land. 
This  is  not  always  obtainable,  or  only  at  great  cost;  and  for 
this  reason  it  might  be  better  to  adopt  filtration,  which 
requires  less  area.  Filtration  may  be  effected  through 

*  Dairy  products  are  considered  by  many  English  cities  the  most  profit- 
able yet  tried;  Birmingham  selling  $20,000  to  $30,000  worth  of  milk  an- 
nually from  its  sewage  farm. 


440  SEWERAGE. 

natural  soil,  if  this  is  fairly  porous,  or  through  specially  pre- 
pared beds  of  sand,  gravel,  coke,  or  other  substances. 

Where  natural  soil  is  used  care  is  taken  to  keep  this  open 
and  free  on  top,  so  far  as  possible;  and  the  sewage  is  turned 
onto  it  at  regular  intervals  and  in  given  quantities,  regardless 
of  the  requirements  of  any  vegetation  thereon.  The  beds 
are  ploughed  into  ridges  and  furrows,  or  are  surrounded  by 
high  banks  and  flooded  to  the  depth  of  several  inches  or  even 
feet.  At  Berlin  the  filtration  area  is  made  into  furrows  18 
inches  deep  by  2  feet  6  inches  wide,  separated  by  ridges  3 
feet  wide.  Crops  may  or  may  not  be  grown  on  the  ridges. 
At  Brocton,  Mass.,  cropping  has  not  been  found  advisable 
for  clarified  sewage;  but  corn  is  grown  to  advantage  in  beds 
upon  which  the  sludge  from  the  settling-tanks  is  placed. 

If  the  soil  is  dense,  the  sewage  may  be  flooded  onto  beds 
surrounded  by  banks.  But  otherwise  the  use  of  furrows  is 
preferred  for  insuring  general  distribution  of  the  sewage.  If 
the  soil  is  very  porous,  there  is  a  tendency  for  all  the  sewage 
to  enter  it  near  the  carrier-outlets.  Under  such  a  condition 
numerous  secondary  carriers  may  be  used,  composed  of  boards 
formed  into  shallow  V-shaped  troughs.  Uniform  distribution 
may  also  be  assisted  by  giving  considerable  slope  to  the 
surface  of  the  beds.  In  both  filtration  and  irrigation  great 
care  must  be  used  to  prevent  the  formation  of  puddles  in 
which  the  sewage  will  stand  and  putrefy.  The  surface  of  the 
ground  in  the  furrows  will  shortly  become  clogged  \viui 
organic  matter,  which  resists  immediate  decomposition,  but 
would  be  broken  down  and  oxidized  if  given  time.  Furrows 
should  then  be  opened  in  the  ridges  where  the  soil  is  probably 
unclogged,  the  earth  being  thrown  into  the  old  furrows.  In 
time  a  considerable  amount  of  undecomposed  organic  matter 
will  collect  throughout  the  interstices  of  the  filter,  and  this 


METHODS    OF    TREATMENT. 


441 


should  then  be  given  a  rest  for  several  days  or  week?,  for  which 
purpose  the  filtration  area  should  be  divided  into  three  or 
more  beds,  one  of  which  is  always  resting.  Those  in  use 
should  be  allowed  to  drain  out  after  each  dose,  that  they  may 
be  re-aerated  ;  the  sewage  generally  flowing  onto  drained  beds 
while  the  ones  previously  used  are  draining.  In  some  small 
plants,  however,  the  sewage  is  received  in  settling-tanks  and 
the  effluent  discharged  upon  all  the  beds  at  intervals  of 
several  hours,  or  even  only  once  a  day. 

Filtration  areas  are  usually  underdrained;  but  if  the  soil 
is  porous  for  a  considerable  depth  and  the  water-table  is  low, 
this  is  not  necessary.  At  the  Meriden,  Conn.,  treatment- 
grounds  sub-drains  were  provided,  but  receive  none  of  the 
effluent,  which  emerges  from  the  river-bank  1 1  to  20  feet 
below  the  outlets  of  the  drains.  Sub-drains  are  generally  of 
3-  to  6-inch  sewer-pipe,  laid  from  3  to  7  feet  deep. 

The  efficiency  of  filtration-grounds  in  practical  use  is 
shown  by  the  following  analyses: 


ANALYSIS  OF  SEWAGE,  SEWAGE  EFFLUENT,  AND  UNPOLLUTED 
GROUND-WATER  FROM  SEWAGE-FIELD  AT  SOUTH  FRAMINGHAM, 
MASS. 


i 

Ammonia. 

Nitrogen  as 

i>  S  ^ 

• 

Color. 

&2  g. 

_c 

rt  qj  rt  c 

Free. 

Albu- 
minoid. 

JD 
S 

Nitrates 

Nitrites. 

h 

u 

0.70 

0,00 

28.30 
19-45 

1-7893 
0-0335 

•3750 
.0039 

4.07 

2.56 

.0080 
.6018 

.0001 
.0006 

"        effluent  at  underdrains.* 

"        "  spring*  
Unpolluted  ground-water  

0.00 
0.00 

7.23 
4.70 

o.oooo 
o.oooo 

.0029 
.0008 

1.77 

O.2O 

•  235° 
.0083 

.0000 
.0000 

*  Little  effluent  comes  from  the  underdrains.     Most  reaches  a  neighboring  brook  through 
springs    The  effluent  at  the  sub-dram  is  apparently  about  35*  ground-water,  and  at  the  sprint 

about  6s%. 


At  Brocton,  Mass.,  where  the  sewage  is  clarified  in  a 
settling-basin  and  then  distributed  to  filtration-beds,  the  fol- 
lowing were  found  to  be  the  average  analyses  of  the  sewage 


442 


SEWERAGE. 


before  and  after  clarification,  of  the  sludge  from  the  basin, 
and  of  the  effluent: 


Ammonia. 

Chlorine. 

Oxygen 
Consumed. 

Free. 

Albuminoid. 

2.5722 
2.3636 

4.4133 
0.0911 

0.8964 
0.5728 
3-7578 
0.0105 

6-34 
6.29 
6.82 
4.80 

5.81 
3.67 
24.69 
O.II 

Sludge                         

Effluent           ...          

At  Gardner,  Mass.,  in  1893,  one  acre  of  bed  was  provided 
for  each  2100  citizens  contributing  sewage.  Two  settling- 
basins  7  X  20  feet  were  used.  At  Oberlin,  Ohio,  about  800 
people,  and  at  Central  Falls,  R.  I.,  noo,  contributed  sewage 
to  each  acre  of  nitration  ground.  At  Plainfield,  N.  J.,  37,000 
gallons,  and  at  Pawtucket,  R.  L,  40,000  gallons  of  sewage  per 
acre  per  day  was  set  as  a  limit.  At  the  latter  place  89%  to  99% 
of  the  albuminoid  ammonia  was  removed. 

If  it  is  desired  to  still  further  economize  space,  artificial 
filters  are  constructed.  These  are  generally  of  sand,  of  an 
"  effective  size  "  *'  of  about  .01  inch,  over  coarse  sand  or  fine 
gravel,  which  in  turn  rests  upon  a  layer  of  medium-sized 
gravel,  at  the  bottom  of  which  the  drains  are  placed.  The 
greater  part  of  the  purification  appears  to  be  done  in  the 
upper  layer,  since  1,118,000  bacteria  have  been  found  per 
gram  of  sand  in  the  upper  inch,  while  at  4  inches  depth 
but  125,000  were  found. f  The  purpose  of  the  finer  top  layer 

*  The  effective  size  of  a  material  "  is  such  that  10  per  cent  of  the  mate- 
rial is  of  smaller  grains  and  90  per  cent  is  of  larger  grains  than  the  size 
given.  The  results  obtained  at  Lawrence  indicate  that  the  finer  10  per 
cent  have  as  much  influence  upon  the  action  of  a  material  in  filtration  as 
the  coarser  90  per  cent."  (24th  Annual  Report  State  Board  of  Health  of 
Mass.) 

f  It  is  probable  that  a  large  percentage  of  the  great  number  of  bacteria 
found  in  the  upper  inch  are  those  strained  out  of  the  sewage,  only  a  few  of 
which  are  nitrifying. 


METHODS  OF   TREATMENT.  443 

is  to  regulate  the  velocity  of  flow,  to  insure  a  more  minute  sub- 
division of  the  water  and  thorough  oxidation,  and  to  support 
the  gelatinous  top  coating  which  materially  assists  in  the  strain- 
ing and  probably  in  the  removal  of  bacteria.  Care  must  be  used 
to  insure  that  in  no  place  does  the  sewage  pass  from  a  coarse  to 
a  fine  sand,  since  organic  matter  would  be  deposited  here  and 
clog  the  filter.  By  having  the  finest  sand  on  top  all  clogging  is 
at  the  surface  where  it  can  be  reached.  For  example,  the  Paw- 
tucket  filters  are  raked  for  i  inch  in  depth  after  every  fifth  dose, 
and  are  thus  kept  free.  At  Woonsocket,  R.  I.,  in  1899,  2  acres  of 
filter-beds  were  constructed  having  18  inches  of  gravel,  on  which 
was  placed  28  inches  of  coarse  sand,  and  on  this  14  inches  of 
medium  sand.  At  Gardner,  Mass.,  16  beds  containing  82,330 
square  feet  were  constructed  by  placing  4  to  5  feet  of  gravel  and 
coarse  sand  on  a  clay  bottom. 

By  intermittent  filtration  through  clean,  coarse  sand  50,000 
to  75,000  gallons  per  day  of  American  sewage  can  be  treated 
on  one  acre, and  97%  to  99%  of  the  organic  matter  therein  removed. 
With  fine  sand  or  sedimentary  deposit  the  same  result  can  be 
obtained  with  30,000  gallons  or  less  per  day  if  care  is  taken  to 
allow  thorough  drainage  between  doses. 

Low  rates  are  obtained  with,  very  fine  soil  because  capillary 
attraction  not  only  prevents  the  actual  passing  of  liquid  at  a  high 
rate,  but  it  retains  a  part  in  the  lower  portion  and  prevents  com- 
plete re-aeration  and  hence  full  oxidation. 

It  is  probable  that  if  sewage  is  applied  without  preliminary 
clarification,  there  will  be  strained  out  on  the  surface  as  much 
suspended  matter  as  though  it  were  collected  in  a  settling  tank; 
in  other  words,  the  same  amount  of  solids  remains  to  be  disposed 
of.  And  collection  on  the  surface  interferes  with  aeration  of  the 
filter  and  even  lessens  the  amount  of  sewage  which  can  be  passed 
through  it.  If  too  much  accumulates  it  will  even  water-proof 
the  surface  in  places  and  cause  pools  of  sewage  to  collect  and  putrefy. 
It  is  therefore  generally  advisable  to  remove  as  much  suspended 


444  SEWERAGE. 

matter  as  possible  before  filtration;  and  the  greater  the  amount 
removed  the  higher  the  rate  of  filtration  possible.  Perhaps 
double  the  rate  can  be  maintained  with  septic  sewage  as  with 
crude;  but  the  clogging  of  the  body  of  the  filter  will  be  more 
rapid,  requiring  frequent  renewal  of  the  sand  because  of  the  fine 
division  of  the  matter. 

The  amount  of  oxygen  introduced  by  each  aeration  of  the 
bed  can  nitrify  only  a  given  amount  of  sewage,  and  if  more  be 
applied  before  re-aeration  an  unsatisfactory  effluent  must  re- 
sult. For  example,  to  nitrify  five  parts  of  nitrogen  per  100,- 
ooo  requires  a  volume  of  air  one-half  as  great  as  that  of  the  sew- 
age treated. 

Nitrification  is  favored  by  certain  constituents  of  soil,  such 
as  carbonate  of  lime,  and  impeded  by  others. 

Polarite  (magnetic  oxide  of  iron  54%,  silica  25%,  lime, 
alum,  magnesia,  carbonaceous  matter  and  moisture  21  )  is  a 
(patented)  granular  substance  used  for  filtration,  but  there 
seems  to  be  little  evidence  that  it  is  more  efficient  than  sand 
of  a  similar  size  of  grain,  or  finely  broken  coke-breeze. 
Polarite  is  generally  placed  in  a  thin  layer  between  an  upper 
and  a  lower  bed  of  sand. 

On  the  care  of  filtration  areas  or  beds  Mr.  Geo.  W.  Fuller 
has  given,  in  the  Report  of  the  Massachusetts  State  Board  of 
Health  for  1893,  the  following  suggestions. 

"  (i)  Systematic  raking,  with  occasional  harrowing  or 
ploughing,  is  very  satisfactory,  particularly  for  coarse  ma- 
terials. 

"  (2)  Systematic  scraping  (removal  of  clogged  material)  at 
regular  intervals  (followed  by  raking  to  loosen  the  material) 
gives  very  good  results,  especially  for  fine  materials. 

"  (3)  Systematic  scraping  when  necessary,  without  raking 
or  harrowing,  is  not  advisable. 

"  (4)  The  efficiency  of  very  fine  material  (clogged  or  not 
clogged)  is  much  increased  by  trenching  with  coarse  material. 


METHODS    OF    TREATMENT.  445 

(Digging  trenches  through  the  bed  and  filling  them  with  other ; 
material,  generally  coarse  sand.] 

"  (5)  Such  trenches  should  contain  carefully  graded  ma- 
terials at  the  bottom  to  prevent  clogging  at  the  junction  of 
the  coarse  and  fine  sand. 

"  (6)  When  new  material  is  put  onto  old  to  replace 
clogged  material  removed  by  scraping,  it  is  always  advisable 
to  mix  the  old  and  the  new  together  in  order  to  prevent 
clogging  at  the  junction  of  layers  of  unlike  capillary  attrac- 
tion. 

"  (7)  The  removal  of  stored  organic  matter  by  resting  for 
a  limited  period  is  sufficiently  great  to  render  this  simple  and 
inexpensive  method  worthy  of  careful  consideration  in  cases 
of  clogging  where  the  available  area  is  not  too  limited. 

"  (8)  It  is  important  that  the  treatment  of  filters  be  such 
that  the  condition  of  operation  be  as  favorable  as  possible 
during  the  cold  winter  weather. 

"  (9)  Great  care  should  be  taken,  especially  in  the  case  of 
filters  of  fine  material,  that  the  capacity  of  the  filter  be  not 
taxed  during  the  winter  months  to  such  an  extent  that  more 
organic  matter  is  stored  throughout  the  sand  than  can  be 
removed  during  the  spring  and  early  summer,  which  is  the 
period  of  highest  nitrification." 

"  Qualitative  deterioration  is  a  serious  matter  in  winter, 
because  when  a  period  of  biological  reconstruction  is  neces- 
sary, nitrification  cannot  be  promptly  re-established,  as  is  the 
case  in  summer,  but  requires  a  period  of  several  weeks  and 
possibly  months."  (Report  Massachusetts  State  Board  of 
Health,  1894.) 

With  reference  to  the  effect  of  cold  and  snow  upon  irriga- 
tion or  filtration  beds,  it  is  found  that  if  snow  falls  before  the 
ground  is  frozen,  there  is  generally  little  trouble;  but  if  the 
ground  becomes  frozen,  the  sewage  usually  freezes  also  if 
flowed  over  a  flat  surface  in  a  thin  stream.  If,  however,  the 


446  SEWERAGE. 

land  be  deeply  furrowed,  there  is  little  danger  of  the  sewage 
freezing.  If  the  land  is  only  slightly  porous,  flooding  to  a 
depth  of  a  foot  or  two  will  give  satisfactory  results.  The 
sewage  should  be  kept  as  warm  as  possible  before  discharging 
onto  beds.  There  is  little  bacterial  action  when  the  tempera- 
ture of  the  sewage  is  below  40°;  the  temperature  most  favor- 
able for  rapid  oxidation  appearing  to  be  90°;  at  about  130° 
it  entirely  ceases. 

Worms  and  burrowing  animals  occasionally  give  trouble 
by  opening  passages  in  the  soil  by  which  unpurified  sewage 
reaches  the  drains.  These  have  been  driven  out  by  flooding 
the  land  once  or  twice  with  very  strong  or  septic  sewage. 

The  sludge  from  the  settling-tanks  is  generally  pumped 
or  flowed  upon  beds  set  apart  for  this  purpose,  which  are 
raked  off  after  each  application  has  dried,  and  the  deposit  is 
left  piled  upon  the  surface  to  be  burned.  In  a  few  plants  the 
sludge  is  taken  by  farmers  for  fertilizer. 

The  cost  of  land  for  irrigation  or  filtration  plants  will  of 
course  vary  with  every  city.  To  a  certain  extent  the  cost 
of  preparing  the  plant  also  will  vary,  depending  upon  the 
character  of  the  soil  and  the  nature  of  its  surface.  A  general 
idea  of  the  cost  of  filtration  plants,  however,  can  be  obtained 
from  the  following  figures: 

At  Spencer,  Mass.,  II  acres  of  partly  wooded  land  was 
prepared,  underdrains  being  placed  5J  feet  deep.  Four-  and 
five-inch  underdrains  cost  1 1  cents  per  foot ;  grubbing,  $50  per 
acre;  excavation,  15  cents  per  cubic  yard;  ploughing  and 
harrowing,  $6  per  acre.  Entire  cost,  $8300. 

At  Marlborough,  Mass.,  20  filter-beds,  settling-tank,  and 
house  cost  $21,720. 

At  Gardner,  Mass.,  1.9  acres,  in  16  beds,  of  gravel 
brought  from  neighboring  banks,  with  two  settling-tanks  each 
7  X  20  feet,  used  by  4000  people  in  1893,  cost  $10,046. 

At   Brocton,    Mass.,    30   acres   in   23    beds,    disposing  of 


METHODS  OF   TREATMENT.  447 

1,000,000  gallons  of  sewage  daily  in  1898,  and  a  receiving- 
reservoir  42  X  n8  feet,  cost  about  $209,000.  Capacity 
2,000,000  gallons  daily. 

At  Bristol,  Conn.,  preparing  6  acres  of  filter-beds  cost 
about  $9000. 

At  Paris,  Tex.,  preparing  5^-  acres,  with  20,179  ^eet  °f 
drains  4  feet  deep,  and  two  settling-basins,  cost  $3730. 

At  Pawtucket,  R.  I.,  the  plant,  comprising  2. 4  acres,  cost 
about  $12,000. 

At  Medfield,  Mass.,  where  no  sub-drains  are  used,  land 
for  disposing  of  25,000  gallons  daily  was  prepared  for  about 
$1000. 

At  Plainfield,  N.  J.,  grading  16  acres,  sub-drains  $  to  7 
feet  deep,  settling-basin  and  pump,  cost  $31,212. 

At  Flemington,  N.  J.,  preparing  5-^-  acres  for  broad  irri- 
gation cost  $5875. 

In  general  it  will  cost  about  $175  to  $450  per  acre  to  pre- 
pare ridge-and-furrow  fields  for  irrigation,  and  $15  to  $50  to 
prepare  fields  for  the  catchment  method. 

The  operating  expenses  at  Oberlin,  Ohio,  (5.25  acres,) 
were  $460  in  1897,  or  17.7  cents  per  capita. 

At  Brocton,  Mass.,  the  operating  expenses  in  1899  were 
$2494,  of  which  $2032  was  for  the  filters  proper  ($17.67  being 
for  handling  snow),  and  the  remainder  for  general  care  of  the 
grounds  and  miscellaneous  expenses. 

At  Meriden,  Conn.,  it  cost  $8.50  per  1,000,000  gallons  to 
care  for  the  filtration  and  irrigation  beds  in  1896. 

At  Plainfield,  N.  J.,  the  cost  of  operating  15  acres  in 
1898  was  $1400. 

On  the  Berlin  sewage  farm  the  labor  averages  one  man  for 
each  77  acres,  there  being  in  all  about  15,000  acres  under 
irrigation. 

In  England  the  force  per  acre  required  to  look  after  irriga- 
tion farms  is  one  man  for  each  6  to  26  acres;  averaging  about 
one  to  each  10  acres. 


SEWERAGE. 


ART.  96.    CONTACT  FILTERS.    SLATE  BEDS. 

An  intermittent  filter  produces  the  purest  effluent  practically 
obtainable  from  sewage.  But  the  rates  are  low  ;  and  in  some  cases 
a  less  pure  effluent  would  be  satisfactory  if  less  area  of  land  could 
be  used.  This  is  found  to  be  impracticable  with  a  fine-grain 
filter,  but  should  theoretically  be  with  a  coarse-grain  one.  The 
latter,  however,  presents  the  practical  difficulty  of  the  uniform 
distribution  of  the  sewage  throughout  the  filter.  If  flowed  on, 
as  in  the  case  of  a  fine-grain  filter,  the  sewage  passes  through  a 
small  section  only,  near  the  point  of  application.  To  meet  this 
difficulty  the  contact  filter  was  devised.  In  this  the  sewage  is 
allowed  to  fill  slowly  a  bed  composed  of  stones  (generally  of  a 
size  varying  from  pea  to  walnut),  to  stand  in  it  while  the  sus- 
pended matter  settles  onto  the  stones  or  collects  on  them  by 
surface  adhesion,  and  is  then  withdrawn  slowly;  after  which 
the  bed  is  allowed  to  remain  empty  for  a  few  hours  to  be- 
come re-aerated  and  permit  oxidation  to  take  place.  In  many 
cases  two  hours  is  allowed  for  each  step,  or  eight  hours  for  a 
cycle. 

The  theory  of  action  of  these  filters  is  as  follows:  "When 
the  effluent  flows  from  a  filter,  air  is  drawn  into  the  filter  again 
and  fills  the  open  space.  Consequently  a  partial  oxidation  of 
the  organic  matter  left  within  the  filtering  material  proceeds 
until  this  oxygen  is  exhausted,  when  the  open  space  is  completely 
filled  with  the  chief  products  of  this  oxidation,  —  namely,  carbonic- 
acid  gas,  marsh-gas,  nitrogen  of  the  air  primarily  present  and 
nitrogen  liberated  during  decomposition,  —  and  the  filter  will  re- 
main with  its  open  space  filled  with  these  gases  until  they  are 
removed  by  the  introduction  of  sewage  or  air.  This  condition 
reached,  the  activity  of  the  oxidizing  and  nitrifying  bacteria  within 
the  filter  ceases  and  anaerobic  actions  begin,  which  change  a 
considerable  portion  of  the  organic  matter  adhering  to  the  filter- 
ing material  into  forms  easily  soluble  and  oxidized  by  the  air 


METHODS  OF  TREATMENT.  449 

introduced  when  the  filter  is  again  flooded."  (Mass.  State 
Board  of  Health,  1899.)  If  these  filters  are  used  in  pairs,  the 
effluent  from  the  "first-contact  filter"  passing  to  the  " second- 
contact  filter,"  the  action  in  the  latter  becomes  almost  wholly 
aerobic. 

A  contact  filter  consists  of  a  pit,  generally  about  4  to  8  feet 
deep.  The  pits  have  generally  been  made  water-tight,  but  this 
does  not  seem  to  be  essential ;  and  experimental  ones  at  Manchester 
were  simply  excavated  from  the  soil,  with  side  slopes  of  2  to  i. 
On  the  bottom  of  the  pit  is  laid  a  series  of  drains  leading  to  a  main 
outlet-pipe,  which  is  provided  with  a  valve  for  regulating  the  flow 
of  sewage  from  the  filter.  The  pit  is  then  filled  with  coke,  coal, 
slag,  cinders,  gravel,  burnt  clay,  glass,  or  other  clean,  insoluble 
material  of  fairly  uniform  size.  Coke  breeze  gives  excellent 
results,  although  it  is  liable  to  slow  disintegration.  The  Man- 
chester experts  obtained  their  best  results  from  clinkers  passing 
through  ij-in.  mesh  and  rejected  by  -J-in.;  and  this  material 
is  recommended  by  the  Massachusetts  Board  of  Health.  Both 
of  these  bodies  of  investigators  found  that  the  contact  beds  had 
at  first  a  water  capacity  of  about  50%,  but  that  this  was  quickly 
reduced  to  about  33%,  at  which  it  remained  constant;  the  re- 
duction being  due  partly  to  the  growth  of  bacterial  jelly  on  the 
surfaces  of  the  filter  material,  partly  to  chaff,  straw,  and  wood 
and  cloth  fibres.  To  prevent  the  filling  of  the  filter  by  sand  or 
other  solid  mineral  matter  a  pit  or  catch-basin  should  be  placed 
above  the  filter,  through  which  the  sewage  should  flow  at  such 
velocity  as  to  carry  on  all  but  heavy  insoluble  matter. 

As  already  stated,  the  operation  of  a  contact  filter  consists 
in  filling  the  filter,  allowing  it  to  remain  full  for  a  fixed  time, 
emptying,  and  allowing  it  to  stand  empty;  two  hours  being 
allowed  for  each  operation  in  many  cases.  It  was  found  at 
Lawrence  that  if  the  sewage  stood  but  two  hours  in  a  single- 
contact  bed  which  was  filled  once  daily,  the  action  during  this 
time  was  anaerobic  only,, the  aerobic  action  taking  place  while 


450  SEWERAGE. 

the  tank  stood  empty.  The  rests  between  doses  should  not  be 
long  enough  to  permit  the  bacteria  to  die  from  lack  of  pabulum, 
but  these  should  be  preserved  in  the  filter  to  work  over  successive 
doses.  For  this  reason  also  the  sewage  should  not  be  allowed 
to  enter  or  leave  the  bed  with  so  great  velocity  as  to  wash  the 
bacteria  out  of  the  filter. 

If  a  contact  bed  is  filled  three  times  a  day,  and  its  interstices 
have  a  volume  one- third  that  of  the  entire  filter,  it  is  evident 
that  the  daily  capacity  of  the  filter  is  its  cubical  contents.  A 
filter  5  feet  deep  could  therefore  treat  37  gallons  per  sq.  ft.  per 
day.  Allowing  for  walls  or  embankments  between  filters  and 
occasional  resting  or  cleaning  of  beds,  it  is  thought  that  25  gals. 
per  sq.  ft.  per  day,  or  say  1,000,000  gals,  per  acre,  can  be  purified. 
If  double  contact  is  employed,  as  it  should  generally  be,  double 
the  area  will  be  required;  or  500,000  gals,  per  acre  per  day  can 
be  rendered  unputrescible;  which  was  the  conclusion  reached  by 
the  Manchester  Commission. 

Double-contact  filters,  6  feet  deep,  in  London  have  removed 
practically  all  the  suspended  matter  and  51%  of  the  dissolved 
putrescible  organic  matter,  when  receiving  600,000  gals,  of  crude 
sewage  per  acre  per  day.  Dibdin  in  1895  filtered  through  3  feet 
of  coke  breeze  the  effluent  from  a  lime-precipitation  plant  at  the 
rate  of  1,000,000  gals,  per  acre  per  day,  the  effluent  from  the  con- 
tact filter  containing  71%  less  albuminoid  ammonia  and  absorb- 
ing 77%  less  oxygen  than  the  precipitation  effleunt  which  was 
applied  to  it. 

In  tests  at  Columbus  with  both  single  and  double  contact, 
the  effluents  from  the  primary  contact  beds  were  putrescible  for 
about  one-third  of  the  time;  and  those  from  the  secondary  con- 
tact filters  were  found  putrescible  about  25  per  cent  of  the  time; 
the  rates  being  from  100  to  300  gals,  per  cu.  yd.  per  day,  which 
was  considerably  reduced  by  periods  of  rest  which  were  allowed 
at  intervals.  The  tanks  were  5  feet  deep  and  the  net  rates  of 
treatment  varied  from  0.5  to  2.38  millions  of  gallons  per  acre  per 


METHODS   OF    TREATMENT.  45 1 

day;  averaging  about  i|  millions.  No  odor  was  noticed  around 
the  niters,  and  when  the  material  was  removed  for  cleaning  the 
only  odor  noticed  was  that  characteristic  of  garden  soil.  The 
percentage  of  suspended  matter  removed  varied  considerably, 
but  averaged  about  40  to  50  from  crude  sewage,  and  60  to  70  from 
settled  or  septic  sewage.  Of  the  organic  nitrogen  the  average 
removal  was  about  35  to  40  per  cent.  Of  the  bacteria  the  percent- 
age of  removal  varied  all  the  way  from  o  to  60,  averaging  about 
40.  Of  the  applied  nitrogen  there  appeared  in  the  nitrified  form 
in  the  effluent  of  the  primary  filters  from  4  to  n  per  cent  and  in 
the  effluents  of  the  secondary  filters  from  17  to  21  per  cent.  An 
important  feature  was  the  uniformity  of  removal  and  the  absence 
of  any  such  unloading  of  stored  material  as  is  characteristic  of 
sprinkling  filters. 

These  filters  had  voids  amounting  to  from  43.1  to  54  per  cent 
of  their  volume  at  the  beginning,  which  was  reduced  to  from  31.9 
to  45.8  at  the  end,  these  voids  being  somewhat  greater  than  had 
been  found  in  other  cases.  Both  limestone  and  coke  were  found 
to  suffer  no  disintegration  or  loss  in  weight  during  nine  months 
of  operation. 

It  was  concluded  that  a  safe  daily  rate  to  produce  a  non- 
putrescible  effluent  from  Columbus  sewage  would  be  in  the  neigh- 
borhood of  600,000  to  700,000  gals,  per  acre  per  day  of  5  foot 
bed.  Aside  from  the  benefits  to  be  derived  from  a  removal  of 
the  suspended  matters,  septic  treatment  offered  practically  no 
advantage  as  an  adjunct  to  contact  filter  treatment;  on  the  other 
hand  no  disadvantages  appeared.  It  appeared  to  be  virtually 
necessary  in  the  successful  operation  of  contact  filters  not  only 
to  encourage  aerobic  action  at  the  expense  of  a  diminished  anerobic 
and  consequently  reducing  action,  but  to  discharge  the  effluent 
from  the  filter  before  the  nitrates  previously  formed  should  have 
been  entirely  reduced.  Thereby  through  the  nitrates  there  is 
obtained  an  active  and  efficient  agent  in  the  protection  against 
ultimate  putrefaction  of  the  effluent. 


45 2  SEWERAGE. 

Thorough  drainage  of  a  contact  bed  is  of  the  first  importance, 
both  in  order  that  time  may  be  saved  in  removing  the  liquid  con- 
tents and  in  order  that  the  period  of  aeration  may  be  as  long  as 
possible.  For  this  reason  also  it  has  been  found  preferable  to 
diminish  the  time  of  emptying  and  filling  from  the  2  hours  orig- 
inally proposed.  At  Columbus  it  was  concluded  that  the  rate 
of  emptying  should  be  as  high  as  possible  without  creating  undue 
mechanical  disturbance  within  the  filter,  from  one-half  hour  to 
an  hour  being  considered  sufficient  for  a  filter  5  feet  deep.  So 
far  as  nitrification  is  concerned,  the  oxidation  or  resting  empty 
stage  is  the  most  important.  On  the 'other  hand,  however,  the 
resting  full  stage  should  be  sufficiently  long  to  secure  as  high  a 
degree  of  clarification  as  is  consistent  with  proper  operation  other- 
wise; but  should  not  be  so  long  as  to  foster  anaerobic  conditions. 

When  the  filling  up  of  the  pores  of  a  bed  results  from  over- 
working and  the  consequent  accumulation  of  organic  matter  and 
bacterial  jelly,  and  not  from  silt  and  other  mineral  matters,  it 
is  generally  preferable  to  restore  the  bed  by  resting  empty  or  work- 
ing at  a  very  low  rate  rather  than  by  removing  the  material  and 
washing  the  same,  since  the  latter  will  remove  the  bacterial  jelly 
which  is  the  agent  of  oxidation,  and  it  will  require  several  days  or 
weeks  to  restore  the  bed  to  conditions  of  full  activity.  Practically 
all  of  these  conclusions,  reached  at  Columbus,  are  confirmed  by 
actual  experience  with  municipal  plants  in  Ohio  and  elsewhere. 

If  no  insoluble  mineral  matter  reaches  a  contact  filter  and  if 
the  material  of  which  it  is  composed  does  not  disintegrate,  it 
should  act  indefinitely,  any  lessening  of  capacity  caused  by  over- 
working being  remedied  by  resting  or  operating  at  low  rates  or 
with  longer  resting  periods.  Such  resting  periods  should  not  take 
place  in  winter,  however,  if  it  can  be  avoided,  on  account  of  the 
lowering  of  the  efficiency  or  even  possible  freezing  caused  by  the 
entrance  of  cold  air.  To  prevent  this,  methods  have  been  adopted 
in  some  small  plants  of  artificially  heating  the  air,  but  the  expense  of 
this  would  seem  to  be  greater  than  the  advantage  derived  warrants. 


METHODS  OF  TREATMENT.  453 

Instead  of  double  contact,  a  septic  tank  and  contact  filter  are 
frequently  used  in  series.  Or  a  contact  filter  or  double  contact 
filtration  may  be  followed  by  a  fine-grain  filter.  The  former 
combination  is  found  at  Plainfield,  N.  J.,  Lakewood,  O.,  and 
other  places.  At  Marion,  O.,  are  combined  a  septic  tank,  contact 
filter  and  sand  filter  operating  in  the  way  named. 

Similar  in  many  respects  to  contact  beds,  and  yet  differing 
from  them  in  both  construction  and  principles  of  operation  are 
the  slate  beds  which  have  been  experimented  with  by  Dibden 
and  others  since  1907.  In  these  the  basin  or  tank  is  filled  with 
superposed  layers  of  slate,  the  layers  separated  one  to  three  inches 
by  means  of  slate  blocks;  the  whole  thus  forming  an  indestructible 
series  of  shelves  on  which  the  suspended  matters  of  the  sewage 
are  deposited  while  the  beds  are  standing  full.  The  operation 
is  practically  the  same  as  that  of  a  contact  bed,  but  the  deposited 
material  collects  in  more  considerable  masses,  forming  compara- 
tively thick  layers  on  the  slate  shelves,  where  it  undergoes  biological 
action  which  is  carried  on  not  by  bacteria  only,  but  also  by  worms 
or  other  low  forms  of  animal  life.  In  addition  to  the  sedimenta- 
tion which  takes  place  on  the  shelves,  the  finer  suspended  and 
colloidal  matter  is  removed  by  surface  adhesion  as  in  contact 
filters.  In  an  experimental  bed  at  Belfast  95^  per  cent  of  the 
suspended  matter  was  removed.  When  the  beds  were  filled  once 
daily  the  albumenoid  ammonia  was  reduced  47  per  cent,  and  34 
per  cent  when  filled  three  times  daily.  In  these,  as  in  the  regular 
contact  beds,  the  material  collecting  on  the  slate  is  worked  over 
slowly,  although  the  bacterial  jelly  of  the  latter  is  not  in  evidence 
in  the  slate  bed  and  there  seems  to  be  a  tendency  to  the  formation 
of  insoluble  humus-like  matter  somewhat  similar  to  that  discharged 
from  the  sprinkling  filter,  a  substance  which  gives  off  no  offensive 
odor  and  is  not  putrescible.  Owing  to  the  construction  of  the 
slate  bed  it  is  a  comparatively  simple  matter  to  remove  practi- 
cally all  this  matter  from  the  slates  or  shelves  by  flushing  water 
through  it. 


454  SEWERAGE. 


ARTICLE  97.    SPRINKLING  FILTERS. 

As  stated  in  the  previous  article,  one  of  the  chief  reasons  for 
intermittently  filling  and  emptying  the  contact  filter  is  the  neces- 
sity of  distributing  the  sewage  matter  uniformly  throughout  the 
filter.  It  is  seen  that  in  the  contact  filter,  however,  the  conditions 
are  alternately  favorable  to  aerobic  and  to  anaerobic  bacteria, 
and  consequently  at  intervals  unfavorable  to  both;  unless  we 
assume  that  both  liquefaction  and  oxidation  are  performed  by 
facultative  bacteria.  Experiments  with  other  kinds  of  filters 
indicate  that  better  results  would  be  obtained  could  the  conditions 
be  maintained  uniformly  favorable  to  one  kind  of  bacteria;  and 
since  the  filter  as  an  appliance  is  better  adapted  to  aerobic  than 
anaerobic  conditions,  continuous  operation  under  the  former  is 
desirable.  To  secure  this  in  coarse-grain  filters  and  at  the  same 
time  obtain  a  uniform  distribution  of  the  sewage,  two  general 
methods  have  been  adopted;  one,  to  cover  a  porous  filter  with  a 
mat  or  layer  of  fine  material  which  can  be  kept  covered  with  an 
inch  or  two  of  sewage  and  will  allow  it  to  trickle  through  at  the 
desired  rate;  the  other,  by  spraying  the  sewage  or  otherwise  dis- 
tributing it  in  drops  over  the  entire  surface.  Experiments  with  the 
former  have  not  often  been  satisfactory,  although  it  is  not  certain 
that  this  method  may  not  yet  be  developed  along  some  more 
effective  lines.  The  scattering  of  the  sewage  uniformly  over  the 
surface  has  been  attempted  by  the  use  of  a  number  of  appliances 
vith  greater  or  less  success.  Among  the  earlier  were  numerous 
parallel  troughs  with  notches  along  their  edges,  through  which 
notches  the  sewage  ran  in  minute  streams  or  drops.  One  of  the 
obstacles  to  proper  distribution  by  this  method  is  the  difficulty  of 
maintaining  the  troughs  absolutely  and  continuously  level,  and 
another  is  the  collection  of  filamentary  and  other  fine  suspended 
matter  in  the  overflow  notches,  or  the  gradual  accumulation  thereon 
of  mycelial  growths.  Somewhat  better  success  was  had  with  dis~ 


METHODS  OF   TREATMENT.  455 

tributing  the  sewage  in  level  wooden  troughs,  protruding  vertically 
from  the  bottom  of  which  were  nails  driven  at  regular  intervals; 
the  sewage  overflowing  the  edges  of  the  troughs  in  a  thin  sheet  and 
following  the  outer  surface  to  the  nails,  from  which  it  dropped 
onto  the  bed  below.  Uniform  and  continuous  distribution  seems 
almost  impossible  by  this  method  also,  for  much  the  same  reasons 
as  those  just  mentioned. 

Believing  the  advantages  of  the  system -warranted  the  cost,  a 
number  of  English  managers  have  adopted  methods  of  distribut- 
ing the  sewage  over  coarse-grain  niters  by  moving  appliances  of 
various  kinds.  Some  of  these  are  in  the  form  of  troughs  over 
which  the  sewage  pours  in  a  thin  sheet,  the  troughs  being  moved 
slowly  over  the  surface  of  the  bed,  either  revolving  around  a 
central  pin,  the  bed  being  circular,  or  traveling  back  and  forth 
from  one  end  of  a  rectangular  bed  to  the  other.  In  the  latter  case 
the  distributing  trough  is  moved  by  outside  motive  power;  the 
revolving  distributor  may  be  moved  by  outside  power  or  by  the 
action  of  the  sewage  itself  acting  under  a  hydrostatic  head.  Among 
the  revolving  distributors  the  more  common  is  one  which  sprays 
the  sewage  from  one  side  of  the  arm,  the  reaction  causing  revolu- 
tion as  in  a  Barker's  mill.  There  seems  to  be  a  general  agreement 
that  the  moving  distributors  would  not  operate  satisfactorily  in 
the  winter  climates  of  the  northern  part  of  the  United  States,  and 
we  believe  no  such  appliances  have  been  employed  here,  even 
experimentally. 

Instead  of  these,  in  this  country  and  in  some  English  plants 
stationary  sprinkler  heads  are  used  which  spray  the  sewage  through 
nozzles  of  various  forms.  At  the  Massachusetts  Institute  of 
Technology  Experimental  Station  there  was  developed  an  addi- 
tional kind  of  distributor  in  which  the  sewage  flowed  in  a  small 
stream  from  a  pipe  or  trough  onto  a  splashing  disk  or  concave 
plate  which  scattered  the  sewage  in  a  spray  similar  to  that  from 
a  nozzle. 

In  all  of  these  the  aim  is  uniform  distribution.     The  material 


456  SEWERAGE. 

of  which  a  coarse-grain  filter  is  composed  is  ordinarily  one  or  two 
inches  in  diameter  and  there  is  little  capillary  attraction  to  dis- 
tribute the  sewage  horizontally,  experiments  at  Waterbury,  Conn., 
having  indicated  that  such  horizontal  distribution  seldom  exceeds 
1 2  inches.  If  one-fourth  the  surface  of  the  bed  should  be  receiving 
no  sewage,  and  one-half  the  remainder  should  receive  it  at  double 
the  average  rate — which  would  be  a  condition  by  no  means 
unusual — the  last-named  portion  of  the  filter  would  be  working 
at  a  rate  2§  times  as  great  as  the  nominal;  and  if  it  could  do  so 
satisfactorily,  then  the  entire  area  could  operate  at  the  same  rate 
and  a  correspondingly  greater  amount  of  sewage  be  treated  per 
acre,  if  uniform  distribution  could  be  secured.  This  is  the  prin- 
cipal problem  remaining  to  be  solved  in  connection  with  the 
sprinkling  filter. 

The  term  just  used,  sprinkling  filter,  is  that  most  commonly 
employed,  because  sprinking  has  so  far  seemed  to  offer  the  best 
solution  of  this  problem  of  distribution.  Probably,  however, 
trickling  or  percolating  would  be  a  more  correct  term,  since  the 
essential  characteristic  is  not  the  method  of  distribution,  but  the 
fact  that  the  distribution  should  be  uniform  at  such  low  rates  that 
the  sewage  will  pass  slowly  in  thin  films  over  the  filtering  material, 
so  that  the  pores  within  it  shall  always  contain  air  for  the  oxidation 
of  the  organic  matter.  "As  the  sewage  percolates  through  the 
filter,  much  of  the  suspended  matter  is  deposited  upon  the  surface 
of  the  particles  of  filtering  material  and  thin  gelatinous  films  are 
formed  about  the  grains  of  material.  As  in  contact  filters,  it  is 
these  films  which  play  an  important  part  in  the  purification 
effected  by  the  filter,  due  to  their  power  of  removing  by  absorption 
a  certain  proportion  of  the  dissolved  organic  matters  contained 
in  the  sewage  and  of  acting  as  oxygen  carriers. 

"Largely  due  to  the  predominance  of  aerobic  conditions  within 
sprinkling  filters,  the  deposited  organic  matter  is  gradually  oxidized 
to  a  condition  in  which  it  has  lost  the  power  in  a  large  measure  of 
adhesion  to  the  particles  of  filtering  material.  During  periods  of 


METHODS    OF    TREATMENT.  457 

rest  the  oxidation  of  deposited  matters  is  very  rapid  and  coincident 
with  the  efficient  drying  out  which  is  afforded  the  filter  under 
favorable  weather  conditions.  Due  to  these  causes,  when  opera- 
tion is  again  resumed,  the  films  of  stable  suspended  matter  crack, 
peel,  and  are  washed  from  the  filters  to  the  temporary  detriment 
of  the  appearance  of  the  effluent,  but  to  the  ultimate  benefit  of 
the  filter.  The  removal  from  the  filter  in  this  manner  of  the 
deposited  suspended  matter  means  a  less  frequent  removal  of 
filtering  material  on  account  of  clogging,  as  compared  with  contact 
filters,  in  which  no  such  unloading  takes  place.  As  the  sewage 
passes  through  the  filter,  constant  contact  of  the  sewage  with  the 
air  is  conducive  to  the  highest  degree  of  aerobic  bacterial  activity. 
During  the  active  period  of  operation  nitrates  and  nitrites  are 
constantly  being  formed  in  the  filters  and  washed  out  in  the 
effluent,  and  serve  in  this  way  as  a  protecting  agent  against  the 
ultimate  putrefaction  of  the  effluent,  as  do  the  considerable  quan- 
tities of  dissolved  atmospheric  oxygen  which  regularly  escape 
absorption  in  passing  through  the  filter.  During  periods  of  rest 
nitrification  increases  in  intensity,  as  is  the  case  in  contact  filters, 
and  the  unstable  organic  matters  which  have  accumulated  in  the 
filter  are  more  or  less  thoroughly  oxidized,  depending  upon  the 
length  of  the  resting  period." — (From  "  Report  on  Sewage  Puri- 
fication at  Columbus,  Ohio,"  by  George  A.  Johnson.) 

In  the  above  quotation  reference  has  been  made  to  periods  of 
rest.  In  order  to  bring  about  the  unloading  of  the  filter,  or 
removal  of  suspended  matter,  which  is  one  of 'the  characteristics 
of  the  sprinkling  filter,  it  has  seemed  best  to  those  at  Columbus 
to  occasionally  rest  each  filter  bed  from  use  for  a  few  days,  as 
explained.  In  experiments  conducted  at  the  Massachusetts 
Institute  of  Technology,  however,  it  has  been  found  best  not  to 
rest  the  bed;  but  that  the  same  unloading  takes  place  voluntarily 
each  spring,  apparently  with  the  warmer  weather  which  induces 
a  more  vigorous  bacterial  growth  and  action. 

Rates  as  high  as  two  or  even  three  million  gallons  per  acre 


458  SEWERAGE. 

per  day  have  been  satisfactorily  treated  on  sprinkling  filters  in 
this  country,  both  at  Columbus  and  at  Reading,  Pa.  It  seems 
probable,  however,  as  in  the  case  of  sand  filters,  that  the  rate 
should  more  correctly  be  expressed  in  terms  of  nitrogen  to  be 
oxidized  than  in  mere  gallons  of  fluid. 

Concerning  the  results  obtained  by  a  sprinkling  filter,  the 
following  conclusions  were  derived  from  the  Massachusetts  Insti- 
tute of  Technology  experiments:  "It  removes  about  one-half  the 
soluble  organic  matter,  yielding  an  effluent  which  is  somewhat 
turbid,  stable,  and  well  oxygenated.  The  organic  matter  present 
has  been  so  worked  over  and  purified  by  the  bacteria  in  the  filter 
as  to  be  non-putrescible.  Judged  by  the  methylene  blue  reduction 
test,  93  per  cent  of  the  samples  of  the  effluent  are  of  such  stability 
as  to  undergo  no  putrefactive  change  when  kept  closed  up  from 
the  air  for  four  days.  Under  ordinary  conditions  of  discharge 
into  open  water  such  an  effluent  would  be  entirely  unobjectionable. 

"With  good  distribution  the  trickling  beds  show  no  appreciable 
tendency  to  clog.  During  the  greater  part  of  the  year  solid 
matter  accumulates  on  the  surfaces  of  the  stones  throughout  the 
bed,  but  when  this  storage  reaches  a  certain  point,  usually  in  the 
early  spring,  the  solids  break  away  and  come  off  in  the  effluent 
in  a  stable  condition.  In  a  period  covering  two  years  the  total 
amount  of  solid  matter  coming  off  balanced  that  going  on.  The 
filtering  material  at  the  end  of  the  experiments  was  in  excellent 
condition  and  showed  no  storage  of  nitrogen." 

It  is  to  be  noticed  that  the  removal  of  suspended  matter  from 
sewage  by  a  sprinkling  filter  is  largely  nominal,  as  there  is  no 
permanent  storing  of  this  and  very  little  if  any  liquefaction;  but 
the  material  removed,  after  being  modified  to  a  non-putrefactive 
form,  is  carried  away  with  the  effluent  in  flakes  or  patches  which 
can  either  pass  out  with  the  effluent  or  be  intercepted  by  a  settling- 
basin.  Owing  to  this  feature  of  the  sprinkling  filter  it  is  necessary 
that  the  underdrainage  be  free  and  open  in  order  that  these  large 
particles  may  find  ready  exit.  In  recent  large  plants  the  drainage 


METHODS  OF  TREATMENT.  459 

system  has  been  so  designed  that  it  may  be  flushed  out  by  a  stream 
from  a  hose  without  removing  the  filtering  material. 

In  most  plants  arrangement  is  made  for  intercepting  the 
suspended  matter  which  leaves  the  filter  in  a  settling-tank  before 
discharging  the  effluent  into  a  stream.  Owing  to  the  large 
particles,  a  comparatively  small  tank  with  rapid  flow  will  serve 
this  purpose,  one  having  a  capacity  of  one  hour's  flow  being  used 
at  Columbus.  The  matter  here  collected  is  not  readily  putrescible; 
but  it  is  still  organic,  and  if  allowed  to  remain  too  long  in  the 
bottom  of  the  tank  it  will  begin  to  putrefy.  It  should  therefore 
be  removed  at  frequent  intervals  and  may  be  used  for  filling  in 
land.  At  Columbus  advantage  is  taken  of  high  water  in  the 
river  to  discharge  this  sediment  directly  into  the  stream  at  such 
periods.  The  amount  of  this  deposit  was  found  at  the  Massa- 
chusetts Institute  of  Technology  Experimental  Station  to  vary 
from  1.5  to  5.7  cubic  yards  per  million  gallons. 

One  of  the  objectionable  features  of  the  sprinkling  filter  is  the 
rapid  lowering  of  temperature  of  the  sewage  when  sprayed  through 
cold  air.  The  effect  of  winter  weather  is  therefore  greater  than 
in  the  case  of  other  filters.  The  Columbus  filters,  for  instance, 
were  started  in  the  winter,  but  it  was  not  until  June  or  July  of 
the  following  year  that  normal  oxidation  became  established; 
whereas  four  to  six  weeks  should  be  sufficient  time  for  the  attain- 
ment of  this.  In  spite  of  this,  however,  no  greater  difficulty  has 
been  experienced  either  at  Reading,  Pa.,  or  at  Columbus,  Ohio, 
in  operating  stationary  sprinkler  filters  through  the  coldest  winter 
weather  than  is  found  with  other  filters;  probably  because  the 
continuous  operation  prevents  a  thorough  chilling  of  the  filter 
surface,  which  chilling  is  possible  during  the  rest  periods  of  inter- 
mittent sand  and  contact  filters. 

In  the  construction  of  a  sprinkling  filter  the  filtering  material 
may  be  placed  in  a  tank  or  pit  or  may  be  erected  in  a  pile  upon 
the  surface  of  the  ground,  the  material  being  retained  within  walls 
of  concrete  or  masonry  of  open  dry  stone  work.  The  last  has  the 


460 


SEWERAGE. 


advantage  of  affording  additional  opportunity  for  aeration  and  is 
ordinarily  cheaper  than  the  other.  As  the  sewage  simply  per- 
colates downward  there  is  no  necessity  for  water-tight  walls.  A 
size  of  particles  between  J  inch  and  ij  inches  is  believed  to  give 
the  best  results  with  sewage  which  has  previously  been  well 
clarified.  The  more  thorough  the  preliminary  clarification  the 
larger  the  grain  wrhich  can  be  used  to  advantage.  Some  European 
authorities  believe  that  uniformity  of  size  throughout  a  bed  is  of 


Maximum 


and  Minimum  Jet 
Angles  for  any  Surface 


4-Lobed  Spreading 

Cone  for 
Square  Area 


FIG.  42. — NOZZLE  FOR  COVERING  A  SQUARE  AREA. 

more  importance  than  the  actual  size  of  grain,  as  this  gives  the 
maximum  interstitial  space  for  the  circulation  of  air. 

The  very  important  problem  of  uniform  distribution  is  largely 
a  mechanical  and  hydraulic  one,  and  considerable  advance  has 
been  made  in  its  solution;  but  entirely  satisfactory  results  have  not 
yet  been  obtained.  An  ordinary  nozzle  directing  spray  vertically 
upward  covers  an  area  of  bed  which  is  circular  in  shape;  and  no 


METHODS   OF   TREATMENT. 


461 


462  SEWERAGE. 

combination  of  circles  can  be  made  to  cover  a  square  bed  without 
overlapping,  or  leaving  uncovered  triangular  spaces,  or  both. 
The  same  is  true  of  the  splashing  disks  previously  referred  to. 
In  1908  a  patent  was  obtained  for  a  nozzle  which,  owing  to  its 
peculiar  shape,  covers  a  square  area  with  its  jet. 

It  is  not  only  the  shape  of  the  wetted  area,  however,  which 
prevents  uniform  distribution,  but  the  fact  that  jets  tend  to  con- 
centrate the  discharge  in  one  or  more  rings  concentric  around  the 
nozzle.  This  also  can  probably  be  overcome  to  a  large  extent  by 
mechanical  construction  of  the  nozzle.  A  method  adopted  in  a 
few  plants  has  been  to  have  the  matter  discharged  under  a  con- 
stantly rising  and  falling  head  (as  by  two  tanks  alternately  filling 
and  emptying  through  the  discharge  pipe),  the  rising  and  falling 
head  causing  the  wetted  area  to  alternately  increase  and  decrease 
in  size,  though  remaining  constant  in  shape.  While  theoretically 
this  last  plan  would  seem  to  promise  well,  experiments  have 
indicated  that  the  result  is  an  even  less  uniform  distribution  than 
with  a  stationary  head.  Theoretically  it  would  appear  that  the 
moving  distributor  which  travels  back  and  forth  across  a  tank 
at  a  uniform  rate  would  give  the  best  distribution,  and  it  is  pos- 
sible that  some  such  plan  will  yet  be  adopted  in  this  country. 

The  nozzles  used  consist  in  the  majority  of  cases  of  a  vertical 
opening  above  which  is  an  inverted  cone  or  similar  surface  which 
sprays  the  sewage  in  a  more  or  less  horizontal  direction,  as  in 
the  Columbus,  Waterbury,  and  Birmingham  nozzles;  or  one  in 
which  the  jets  issue  from  several  openings  placed  at  an  angle  with 
the  vertical,  as  in  the  Salford.  One  of  the  chief  difficulties  in 
designing  a  satisfactory  nozzle  is  obtaining  a  sufficiently  small 
opening  to  furnish  a  discharge  at  the  desired  low  rate,  and  at  the 
same  time  to  have  it  of  such  size  and  shape  that  it  will  not  clog 
with  fine  suspended  matter. 

Probably  the  most  exhaustive  tests  of  nozzles  and  other  dis- 
tributors which  have  been  made  in  this  country  were  those  con- 
ducted at  the  Massachusetts  Institute  of  Technology  Experimental 


METHODS  OF   TREATMENT. 


463 


Station.     As  before  stated  there  was  devised  at  this  station  a 
method  of  distributing  by  splashing  disks  or  saucer-shaped  plates 


BIRMINGHAM"  (NEW) 


FIG.  44.— TYPES  OF  SEWAGE-SPRINKLING  NOZZLES. 

into  which  sewage  was  allowed  to  flow  in  a  continuous  small  stream. 
Experiments  were  made  with  numerous  styles  and  sizes  of  these, 


464  SEWERAGE. 

and   the  following   conclusions   concerning   them   were   derived 
therefrom: 

1.  The  discharge  on  each  sprinkler  should  be  in  the  neighborhood  of  four 
gallons  per  minute;   this   means,  for  a  two-million  gallon  rate,  340  sprinklers  per 
acre,  with  a  distance  between  sprinklers  of  about  n  feet. 

2.  The  head  between  the  distributing  trough  or  pipe  and  the  filters  should  be 
as  great  as  possible;    2  feet  is  inadequate,  4  feet  gives  fair  results,  and  6  feet  is 
better. 

3.  The  head  on  the  sprinklers  should  be  from  2  to  4  feet.    The  best  subdivision 
of  available  total  head   can   probably  best    be  determined  by  experiments  with 
the  disks  to  be  used  in  each  individual  case. 

4.  A  simple  concave  disk  of  metal  seems  to  produce  the  best  efficiency. 

5.  The  best  diameter  for  the  disks  appears  to  be  3  inches.     For  low  rates  of 
discharge  smaller  disks  are  better,  and  for  very  high  rates  or  very  high  heads 
larger  ones  may  be  more  suitable. 

6.  Unless  the  disk  be  too  large    it  is  of  advantage  to  increase  its  concavity 
as  much  as  possible.     Of  3-inch  disks,  that  having  a  concavity  corresponding  to  a 
radius  of   2   inches  proved   most   satisfactory.     The   radius  of  curvature   might 
profitably  be  increased  toward  the  limiting  value  of  i$  inches,  which  would  make 
the  disk  a  hemisphere.     With  larger  disks  larger  radii  of  curvatures  are  necessary. 

A  method  of  expressing  efficiency  of  sprinklers  was  found 
necessary,  and  the  one  devised  by  Mr.  Earle  B.  Phelps  is  sug- 
gested for  general  use  for  this  purpose.  In  this  method  the  area 
covered  by  the  jet  is  divided  into  small  collecting-tanks,  in  which 
is  collected  the  falling  sewage.  In  this  way  the  amounts  falling 
at  various  known  distances  from  the  center  or  nozzle  may  be 
determined.  If  the  quantity  <2,  collected  in  each  small  collecting- 
tank  be  multiplied  by  the  distance  D,  of  its  center  from  the  center 
of  the  nozzle,  the  products  will  be  proportional  to  the  total 
amounts  distributed  in  annular  spaces  entirely  surrounding  the 
nozzle  and  at  the  distance  D  from  it.  Plotting  quantities  Q  as 
ordinates  and  the  corresponding  D  values  as  abscissas,  we  obtain 
a  curve  showing  the  relative  distribution  of  the  sewage  along  the 
radius.  This  curve  is  shown  at  A  in  the  diagram.  It  shows  the 
rate  of  discharge  per  unit  area  at  any  point  whose  distance  from 
the  center  is  known,  and  is  called  the  "  curve  of  radial  distribu- 
tion"; and  an  ordinate  to  this  at  any  distance  from  the  center 
or  point  of  origin  shows  the  rate  of  discharge  at  all  points  on  a 


METHODS  OF   TREATMENT. 


465 


circumference  at  that  distance  from  the  center.  The  products 
DXQ  are  also  plotted  as  ordinates  with  the  corresponding  D 
values  as  abscissas  and  the  curve  B  is  obtained,  called  the  "curve 
of  distribution."  The  total  area  under  this  curve  represents 


4567 
Radial  Distance 


10 


FIG.  45. — DISTRIBUTION  CURVES. 

the  total  discharge  from  the  sprinkler.  Perfect  distribution,  being 
that  at  a  uniform  rate  throughout  the  wetted  area,  would  be  repre- 
sented by  a  straight  line;  and  this  line  would  enclose  below  it 
an  area  representing  the  total  discharge  from  the  sprinkler,  or 
the  same  as  that  below  B.  The  departure  of  the  triangle  last 
formed  from  the  curve  B  shows  the  variation  of  the  nozzle  from 
perfect  distribution.  The  area  between  these  two  is  there- 


466  SEWERAGE. 

fore  the  measure  of  that  variation.  This  is  called  the  "excessive 
discharge  "  E.  The  coefficient  is  then  represented  by  the  ratio 
between  total  discharge  and  total  discharge  minus  excessive 

rp Tf 

discharge;  or  by  — — — .   If  E  becomes  zero  the  coefficient  is  one, 

or  perfection.  This  coefficient  Mr.  Phelps  calls  the  "distributor 
coefficient." 

This  gives  a  measure  of  the  uniformity  of  distribution  within  a 
circular  area.  This,  however,  must  be  modified  to  express  the 
relation  of  the  actual  distribution  to  perfect  distribution  over  the 
entire  area  of  the  filter.  If  each  nozzle  discharges  a  certain 
amount,  and  a  certain  quantity  per  area  has  been  determined 
upon,  the  number  of  nozzles  per  acre  and  their  distance  apart  are 
fixed.  The  most  effective  arrangement  of  these  is  to  place  them 
alternating  rather  than  directly  opposite  each  other;  and  if  so 
arranged,  with  the  circular  wetted  areas  exactly  tangent,  there 
still  remains  about  10  per  cent  of  the  area  which  is  not  wetted. 
(With  special  nozzles  covering  a  square  area  the  whole  bed  may, 
theoretically,  be  wetted.)  It  may  also  be  that  the  spread  of 
the  nozzle  is  not  sufficient  or  is  too  great  to  produce  exact  tangency. 
Correcting  the  distribution  coefficient  for  these  various  conditions, 
we  obtain  a  corrected  coefficient. 

The  best  results  of  the  Birmingham  nozzle,  as  determined  by 
the  tests  above  referred  to,  gave  corrected  coefficients  from  0.7 
to  0.8.  The  Columbus  nozzle  gave  corrected  coefficients  of  0.26 
to  0.30.  The  Waterbury  nozzle  gave  a  maximum  corrected 
coefficient  of  about  0.22.  The  new  Salford  gave  0.67  as  the 
best  corrected  coefficient  and  the  old  Salford  0.41.  The  best 
splashing  disk  (also  called  gravity  distributor)  gave  0.62.  These 
results  were  obtained  by  tests  with  clear  water.  Actual  service 
has  apparently  indicated  that  the  Birmingham  nozzle,  which 
gave  the  highest  efficiency,'  is  more  liable  to  clog  and  act 
irregularly  than  is  the  Columbus  nozzle.  This  matter  of 
continuous  action  is  fully  as  important  as  distribution  co- 


METHODS  OF  TREATMENT.  467 

efficient.  It  is  apparent  that  the  perfect  distributor  has  not 
yet  been  discovered;  and  that  when  it  has  been  the  capacity 
of  sprinkling  niters  may  be  increased  very  largely  over 
that  now  attainable. 


ART.  98.    DISINFECTION. 

Disinfection,  or  the  direct  destruction  of  bacteria,  may  theo- 
retically be  accomplished  by  one  of  several  methods.  Those 
proposed  include  heat,  lime,  acids,  ozone,  chlorine  and  its  com- 
pounds, copper  and  its  compounds,  and  a  number  of  other  sub- 
stances, including  permanganates.  Heat  is  used  for  sterlizing  or 
disinfecting  small  amounts  of  liquids,  but  would  be  entirely  too 
expensive  for  sterlizing  the  enormous  quantities  of  sewage  which 
must  be  treated;  at  least  by  any  method  yet  suggested.  The 
amount  of  coal  required  to  raise  a  million  gallons  of  sewage  from 
60  degrees  to  the  boiling-point  would  be  about  40  tons,  worth, 
say,  $100.  It  has  been  proposed  to  recover  a  part  of  the  cost 
by  the  sale  of  free  ammonia  distilled  while  boiling  the  sewage. 
The  total  amount  of  free  ammonia  in  a  million  gallons  will 
probably  average  from  50  to  100  pounds  and  this,  if  concentrated 
to  commercial  strength  of  28  per  cent  would  bring  about  40  cents 
per  pound.  It  would,  however,  probably  be  impossible  to  recover 
all  of  this.  The  net  cost  would  therefore  probably  be  at  least 
$75  per  million  gallons. 

Lime  is  apparently  too  weak  a  germicide  for  the  purpose;  the 
large  quantities  used  in  chemical  precipitation  apparently  having 
little  effect  upon  bacteria  except  to  precipitate  them  with  the  sludge. 
The  use  of  acid  promises  better  than  that  of  alkalies,  since  bacteria, 
especially  those  of  typhoid  and  cholera,  are  more  sensitive  to 
acids.  Different  investigators  have  found  from  0.04  to  0.08  per 
cent  of  sulphuric  acid  to  be  fatal  to  pathogenic  bacteria.  The 
cost  of  the  smaller  amount  of  sulphuric  acid,  however,  would  be 
between  $150  and  $175  per  million  gallons.  It  is  possible  that 


468  SEWERAGE. 

with  favorable  conditions  even  smaller  amounts  would  be  sufficient 
to  produce  a  very  high  rate  of  sterilization,  but  on  the  other  hand 
any  alkali  in  the  sewage  must  first  be  neutralized  before  any  effect 
could  be  obtained  from  the  acid.  Here  again  the  expense  is 
prohibitive.  Ozone  has  been  used  with  more  or  less  success  for 
sterilizing  drinking  water  and  could  undoubtedly  be  used  with 
sewage  also;  although  it  is  possible  that  it  would  not  be  effective 
should  the  sewage  carry  large  particles  of  suspended  matter. 
Here  again  the  expense,  however,  would  seem  to  be  prohibitive, 
as  it  has  not  yet  been  found  possible  to  sterilize  water  econom- 
ically by  this  method,  and  the  amount  of  ozone  required  for 
sterilizing  sewage  would  be  much  greater  than  in  the  case  of 
water. 

The  substances  which  promise  most  favorably,  both  as  to 
effectiveness  and  cheapness,  are  the  compounds  of  chlorine  and 
copper.  The  latter  has  been  used  successfully  as  an  algicide 
for  clearing  reservoirs  and  lakes  of  vegetable  growths;  and  it  is 
known  that  copper  salts  and  especially  copper  sulphate  are  highly 
disinfectant  in  comparatively  small  quantities.  Probably  the 
most  exhaustive  experiments  which  have  been  made  with  copper 
sulphate  are  those  conducted  by  the  Ohio  State  Board  of  Health 
at  Marion,  Lancaster,  Westerville,  and  other  cities.  At  the  same 
time  experiments  wTere  conducted  with  the  use  of  chloride  of  lime 
or  bleaching  powder.  Summarizing  these  experiments  the  State 
Board  reported:  "Very  satisfactory  results  were  obtained  with 
both  copper  sulphate  and  chloride  of  lime.  Copper  sulphate 
appeared  the  more  limited  as  regards  its  adaptability  to  practical 
conditions  in  that  its  efficiency  is  perhaps  more  dependent  upon 
a  high-grade  sewage  effluent,  together  with  a  required  storage 
point  of  at  least  three  hours.  Chlorine  as  bleaching  powder,  on 
the  other  hand,  requires  less  storage  and  is  less  susceptible  to 
organic  matter. 

"The  indications  drawn  from  these  studies  were,  briefly,  that 
a  sewage  effluent  of  a  purity  equal  to  that  from  efficiently  operated 


METHODS  OF    TREATMENT.  469 

intermittent  sand  filters  may  be  disinfected  as  regards  B.  coli 
by  the  use  of  thirteen  parts  per  million  of  copper  sulphate  (108 
pounds  per  million  gallons)  with  a  storage  of  treated  effluent  of 
about  three  hours  and  at  a  cost  for  chemicals  of  about  $6.48  per 
million  gallons.  Similar  results  with  chloride  of  lime  required 
about  four  parts  per  million  of  available  chlorine  (133  pounds  per 
million  gallons  of  bleaching  powder  containing  25  per  cent  avail- 
able chlorine),  under  one  hour's  storage  at  a  cost  of  $3.32  per 
million  gallons. 

"With  less  highly  purified  effluents,  greater  quantities  of  sul- 
phate were  required,  40  parts  per  million  (334  pounds  per  million 
gallons),  applied  to  the  Westerville  continuous  contact  filter 
effluent  removing,  however,  about  99.3  per  cent  of  the  acid  forming 
colonies  under  about  one  hour's  storage  and  at  a  cost  for  chemicals 
of  about  $20  per  million  gallons.  Chloride  of  lime,  on  the  other 
hand,  under  the  application  of  lesser  quantities  appeared  to  be 
quite  efficient  for  effluents  of  less  stability  than  those  from  sand 
filters,  results  from  the  putrescible  Marion  contact  filters  showing 
a  removal  of  100  per  cent  of  fermenting  organisms  with  the  use 
of  five  parts  per  million  of  applied  chlorine  at  a  cost  for  chemicals 
of  $4.15  per  million  gallons." 

Larger  amounts  were  required  for  septic  tank  effluents,  as 
high  as  25  p'arts  of  available  chlorine  per  million  gallons  removing 
99.3  per  cent  of  fermenting  organisms.  There  were,  however, 
indications  that  more  thorough  settling  of  the  septic  effluent  or 
the  addition  of  larger  amounts  of  chlorine  or  both  would  have 
raised  the  percentage  to  practically  100.  The  prices  given  above 
were  for  chemicals  only.  The  board  of  health  has  prepared  an 
estimate  based  upon  the  cost  of  both  chemicals  and  labor,  but  not 
including  interest,  depreciation,  etc.  This  gives  the  annual  cost 
of  quite  thoroughly  disinfecting  crude  sewage  at  $18.55  Per  IOO° 
gallons  per  day.;  that  of  the  effluent  from  contact  filters  at  $11.77 
per  day  for  copper  sulphate  or  $2.73  for  chloride  of  lime;  the 
effluent  from  sand  filters  at  from  $4.86  to  $6.93  with  copper 


470  SEWERAGE. 

sulphate  and  from  $2.43  to  $5.78  for  chloride  of  lime;  and  the 
effluent  from  septic  tanks  at  $8.83  with  chloride  of  lime. 

Still  more  extensive  experiments  have  been  conducted  with 
chloride  of  lime  by  Mr.  Earle  B.  Phelps,  at  the  Experimental 
Station  of  the  Massachusetts  Institute  of  Technology,  at  Red 
Bank,  N.  J.,  and  at  Baltimore,  Md.;  the  Red  Bank  experiments 
being  conducted  on  250,000  gallons  per  day  of  septic  effluent  and 
those  at  Baltimore  on  the  effluent  from  a  sewage  previously  treated 
by  a  septic  tank  and  trickling  filter.  It  was  found  that  the 
Baltimore  effluent  could  be  satisfactorily  disinfected  by  the  use 
of  about  75  pounds  of  bleaching  powder  per  million  gallons,  the 
bacterial  efficiency  of  this  being  95  per  cent,  and  the  combined 
bacterial  efficiency  of  sprinkling  filter  and  bleaching  powder 
being  between  98  and  99  per  cent.  This  amount  of  bleaching 
powder  represents  three  parts  per  million  of  available  chlorine. 
The  cost  of  such  treatment  is  estimated  at  $1.00  to  $1.50  per 
million  gallons.  To  remove  98  per  cent  of  total  bacteria  from 
crude  sewage,  it  was  determined,  would  require  from  five  to  ten 
parts  per  million  of  available  chlorine  and  cost  from  $1.50 
to  $3.50  per  million  gallons.  It  was  also  found  from  these 
experiments  that  the  disinfection  of  septic  sewage  required  from 
ten  to  fifteen  parts  of  available  chlorine.  However,  it  would 
appear  that  it  would  be  very  advantageous  to  disinfect  the 
sewage  before  septic  treatment  rather  than  after;  this  requiring 
less  chlorine  and  being  equally  effective  in  destroying  the  patho- 
genic bacteria,  but  leaving  in  the  effluent  the  liquefying  and  nitrify- 
ing bacteria  to  continue  the  purification  after  discharge  into  the 
stream. 

Mr.  Phelps  has  prepared  a  table  of  estimated  costs  of  treating 
sewage  and  effluents  of  various  kinds  with  bleaching  powder,  these 
figures  being  based  upon  a  plant  having  a  capacity  of  five  million 
gallons  per  day,  the  cost  given  being  that  per  million  gallons. 
The  treatment  is  classified  according  to  amounts  of  available 
chlorine  used,  and  these  are  considered  to  apply  as  above  stated, 


METHODS    OF   TREATMENT. 


471 


namely,  from  two  to  five  parts  for  filter  effluents  of  varying  quality; 
from  five  to  ten  parts  for  sewages,  and  from  ten  to  fifteen  parts 
or  more  for  septic  sewages. 

TABLE  No.  28. 

DISINFECTION   OF    SEWAGE   AND  EFFLUENTS. 


Bleach 

Cost  per  Million  Gallons. 

Average 
Chlorine 
Parts  per 
Million. 

per  Mil- 
lion Gal- 
lons 
(Approxi- 
mate). 

Time  of 
Contact 
Hours. 

Fixed. 

Operating. 

Storage 
Tanks. 

Other 
Fixed 
Charges. 

Bleach- 
ing 
Powder. 

Labor. 

Power. 

Total. 

i 

2- 

50 

$O    IO 

$O   O2 

$o  30 

$O    IO 

$<->     C2 

2 

CQ 

2    s 

ex 

04 

60 

IO 

70 

3 

75 

1.6 

.04 

.90 

.10 

$0.02 

I.  II 

4 

100 

1.2 

.03 

.07 

1.20 

.10 

.02 

1.42 

5 

I25 

0.8 

.03 

.08 

I.50 

.10 

.03 

1.74 

10 

250 

°-5 

.02 

.16 

-15 

.06 

3-39 

15 

375 

0-5 

.02 

.24 

4-5° 

.20 

.09 

5-05 

It  is  seen  that  the  costs  of  disinfecting  by  bleaching  powder  given 
by  Phelps  are  only  about  one-third  to  one-fifth  of  those  given  by 
the  Ohio  Board  of  Health.  A  considerable  part  of  this  difference 
is  probably  due  to  the  difference  in  size  of  the  plants — five  million 
gallons  per  day  in  one  case  as  compared  to  from  40,000  to  160,000 
gallons  per  day  in  the  Ohio  plants.  Moreover,  the  bleaching  powder 
is  assumed  in  the  Ohio  report  to  contain  but  25  per  cent  available 
chlorine,  and  to  cost  2^  cents  per  pound.  An  estimate  of  the 
cost  of  a  plant  for  one  of  these  towns,  with  an  assumed  flow  of 
600,000  gallons  per  day,  is  given  as  $151  exclusive  of  arrangements 
for  supplying  water  to  dissolve  the  chloride  of  lime. 

In  applying  chloride  of  lime  or  other  disinfectant,  time  and 
thorough  mixing  are  necessary.  Heat  also  plays  some  part  in 
the  effectiveness  of  action.  Certain  experiments  seem  to  indicate 
that  it  is  better  that  the  mixing  of  the  disinfectant  with  the  sewage 
should  take  place  somewhat  slowly  and  should  continue  through- 


472  SEWERAGE. 

out  a  period  of  an  hour  or  more  before  the  effluent  is  diluted 
by  discharge  into  a  stream. 

The  action  of  the  chlorine  is  probably  through  the  free  nascent 
oxygen  which  it  liberates  from  the  water  in  which  it  is  dissolved, 
the  oxygen  destroying  the  bacteria  in  the  same  manner  as  ozone 
would.  It  is  for  this  reason  that  organic  impurities  in  the  sewage 
increase  the  amount  of  chlorine  required,  since  a  considerable 
part  of  the  oxygen  would  be  taken  up  by  these  rather  than  be 
used  in  destroying  the  bacteria.  Chlorine  is  also  obtainable  as 
chlorine  gas,  and  as  oxychlorides,  these  existing  in  three  forms, 
C^O,  C^Oa,  and  C1O2.  Any  of  these  could  be  used  as  a  dis- 
infectant, but  the  cost  is  greater  than  that  of  bleaching  powder. 
Potassium  and  sodium  permanganate  have  been  used  for  the 
oxidation  of  organic  matter  in  streams  and  in  sewage  as  laboratory 
experiments.  Apparently  the  only  objection  to  their  use  is  that 
it  is  more  expensive  than  the  chlorine  compounds,  without  any 
greater  efficiency. 

Bleaching  powder  is  manufactured  chiefly  by  the  electrolytic 
process  at  Niagara  Falls  and  can  be  purchased  at  about  one  cent 
per  pound  guaranteed  40  per  cent  available  chlorine.  This  cost 
of  2\  cents  per  pound  of  available  chlorine  is  equivalent  to  21  cents 
per  million  gallons  for  each  part  of  available  chlorine.  It  has 
been  suggested,  and  indeed  some  small  plants  have  been  operated 
upon  the  principle,  that  the  chlorine  might  be  manufactured  from 
caustic  lime  by  the  application  of  electric  current.  As  this  is 
practically  the  method  employed  in  the  manufacture  of  bleaching 
powder  at  Niagara  Falls,  where  current  is  unusually  cheap,  the 
process  conducted  on  an  enormous  scale,  and  the  bleaching  powder 
merely  a  by-product,  it  does  not  seem  at  all  probable  that  it  will 
be  possible  to  create  chlorine  electrolytlcally  in  the  comparatively 
small  quantities  required  in  sewage  disposal  plants  as  cheaply 
as  it  can  be  purchased.  There  is  an  advantage  in  the  chlorine 
gas  generated  in  the  sewage  itself,  however,  in  that  it  is  more 
powerful  and  more  fully  available  than  the  chlorine  in  bleaching 


METHODS    OF    TREATMENT.  473 

powder,  and  it  is  possible  that  some  method  may  be  devised  for 
the  use  of  electricity  for  generating  chlorine  in  the  sewage  itself. 

The  use  of  electricity  to  decompose  sea-water,  or  a  solution  of 
magnesium  and  sodium  chlorides,  has  been  used  in  this  country 
under  the  name  of  the  Woolf  process  at  Brewsters,  N.  Y.,  and 
at  Danbury,  Conn.,  but  in  1895  the  latter  place  was  enjoined 
from  discharging  the  effluent  from  this  treatment  into  the  Still 
river,  and  adopted  filtration  in  its  place.  At  Brewsters  1000 
gallons  of  water  containing  160  pounds  of  salt  was  subjected  to 
an  electric  current  of  about  700  amperes  and  five  volts,  the 
positive  electrode  being  of  copper  plated  with  platinum  and  the 
negative  of  carbon,  a  4-H.P.  dynamo  being  used.  One  part  of 
this  solution  was  used  in  100  parts  of  sewage,  or  $3.20  of  salt 
to  each  one  million  gallons.  Practically  the  same  process  was 
used  in  Bombay  in  1897,  but  abandoned  after  four  months'  trial, 
it  being  found  that  the  same  amount  of  free  chlorine  could  be 
obtained  with  chloride  of  lime  at  one-half  the  cost. 

It  is  noticed  that  Phelps  refers  to  the  destruction  of  only  98  to 
99  per  cent  of  the  bacteria.  If  is  found  that,  whatever  method  of 
disinfection  or  sterilization  be  employed,  the  use  of  comparatively 
small  amounts  will  effect  the  purification  up  to,  say,  95  per  cent; 
that  double  this  amount  would  be  required  to  increase  this  to 
98  or  99  per  cent;  and  that  two  or  three  times  this  latter  quantity 
would  be  required  for  complete  sterilization,  if  indeed  this  last 
would  be  possible  with  any  practicable  amount.  This  phe- 
nomenon was  termed  by  George  C.  Whipple  as  that  of  a  "  re- 
sistant minority,"  there  apparently  being  a  certain  very  small 
percentage  of  bacteria  in  all  sewages  which  are  destroyed  very 
much  less  readily  than  any  of  the  others.  Further  investigation 
is  necessary  to  determine  whether  or  not  this  small  resistant 
minority  contains  any  pathogenic  bacteria.  There  are  some 
reasons  for  thinking  that  it  does  not.  At  any  rate  the  great 
addition  to  the  cost  required  for  destroying  this  last  one  per 
cent  would  not  ordinarily  be  justified  by  the  results  obtained. 


474  SEWERAGE. 

ART.  99.    MISCELLANEOUS  METHODS. 

Special  conditions  or  special  ideas  concerning  sewage  puri- 
fication have  naturally  led  to  the  designing  and  in  some  cases 
constructing  of  a  number  of  variations  on  •  the  methods  and 
devices  described  in  the  previous  articles.  One  of  these  is  the 
"wave  filter,"  which  has  been  used  in  at  least  three  or  four  plants 
in  this  country.  At  Kenton,  Ohio,  are  three  wave  filters,  each 
10  feet  wide  and  100  feet  long,  filled  with  broken  stone  and  pea 
coke,  the  stone  being  from  i  to  3  inches  in  diameter;  the  depth 
of  the  filtering  material  decreasing  gradually  from  2  feet  at  the 
upper  end  of  the  filter  to  6  inches  at  the  toe.  Dosing  devices 
discharge  the  sewage  at  the  upper  end  of  these  filters  into  each, 
in  rotation,  and  the  sewage  passes  in  waves  or  sudden  flushes 
through  the  filter  to  the  toe,  where  it  flows  through  a  number  of 
2X8J-inch  openings  into  an  effluent  channel.  The  dosing 
intervals  were  approximately  five  minutes.  The  filters  are 
supposed  to  serve  to  aerate  the  sewage  passing  through  them 
and  to  remove  by  straining  and  surface  adhesion  a  large  part 
of  the  suspended  matter,  which  is  oxidized  after  the  draining  of 
the  filter  at  the  termination  of  each  dose.  It  was  believed  that 
the  wave  action  would  displace  the  carbonic  acid  and  nitrogen 
gases  which  would  be  formed  in  the  pores  during  the  periods  of 
rest.  The  material  was  removed  from  each  filter  twice  a  year 
and  spread  on  adjacent  land  in  thin  layers  where  exposure  to 
sun,  wind,  and  rain  sufficed  to  restore  it  to  such  condition  that, 
after  screening,  it  was  suitable  for  use  again.  The  general 
experience  here  and  in  other  plants  appears  to  have  been  that 
these  filters  have  not  developed  the  efficiency  expected,  and  their 
use  has  been  quite  limited. 

In  the  Scott-Moncrieff  " cultivation  filter"  the  sewage  passes 
upward  through  gravel  or  broken  stone,  leaving  the  solid  matter 
behind,  but  carrying  with  it  all  matter  liquefied  from  sludge 
previously  deposited.  Here  the  aim  is  to  combine  both  lique- 


METHODS  OF  TREATMENT.  475 

faction  and  nitrification  in  the  same  filter,  the  liquefying  anaerobes 
being  segregated  in  the  lower  part,  the  nitrifying  bacteria  in  the 
upper,  although  the  former  class  of  bacteria  sometimes  occupies 
the  entire  filter. 

A  somewhat  similar  idea  was  used  in  an  experimental  septic 
tank  by  the  Massachusetts  State  Board  of  Health;  a  septic  tank 
being  filled  with  coarse  stone  with  the  idea  that  these  would 
assist  in  retaining  permanently  a  larger  proportion  of  the  liquefy- 
ing bacteria,  and  that  less  intermingling  of  the  sludge  with  the 
effluent  would  take  place.  While  there  are  some  advantages 
found  both  in  this  and  the  Scott-Moncrieff  tank,  the  cost  and 
difficulty  of  removing  and  cleaning  all  the  filtering  material  at 
the  more  or  less  frequent  intervals  when  the  sludge  requires 
removal  seems  a  serious  objection. 

The  idea  of  forcing  air  into  a  filter  to  secure  more  rapid  and 
thorough  oxidation  has  been  made  the  basis  of  a  number  of  types 
of  filters.  Colonel  Ducat  in  England  constructed  a  number  of 
filter  beds  with  porous  walls  and  bottom,  with  the  idea  of  supply- 
ing more  oxygen  for  nitrification.  The  same  idea  is  found  in  the 
sprinkling  filters  contained  within  dry  stone  walls,  as  previously 
described.  One  objection  found  to  this  is  that  the  large  amount 
of  outer  air  which  enters  the  filter  in  winter  cools  the  sewage 
below  the  temperature  most  favorable  to  bacterial  action.  Low- 
cock,  an  Englishman,  placed  in  a  sand  filter  a  layer  of  coarse 
gravel  at  about  one-third  of  its  depth  from  the  top,  and  through 
this  gravel  laid  a  number  of  perforated  pipes,  through  which  a 
blower  forced  air  continuously,  the  mingled  air  and  sewage 
passing  downward  through  4  feet  of  coke  or  gravel  to  subdrains; 
only  a  slight  pressure  being  required  in  the  blower.  The  object 
of  this  construction  was  to  render  unnecessary  the  rest  and 
aerating  of  sand  filters.  The  same  result  was  the  aim  of  Colonel 
Waring,  who  established  at  Willow  Grove  Park,  Philadelphia, 
and  at  Homewood,  Brooklyn,  filters  in  which  air  was  forced 
through  porous  tile  laid  in  the  bottoms  of  the  filters;  the  former 


476  SEWERAGE. 

plant  treating  strained  sewage  at  the  rate  of  640,000  to  800,000 
gallons  per  acre  per  day;  the  latter  treating  245,000  gallons  per 
acre  of  strainer  and  filter  combined. 

Another  and  cheaper  method,  although  less  positive  in  action, 
is  the  use  of  ventilating  hoods,  held  towards  the  wind  by  vanes, 
the  hoods  being  fastened  to  the  top  of  vertical  pipes  which  connect 
with  and  discharge  the  air  into  the  under  drains;  the  under 
drains  being  trapped  so  that  the  air  will  be  forced  to  rise  upward 
through  the  filter,  rather  than  escape  through  the  outlet.  A 
calculation  based  on  Dr.  Rideal's  experiments  indicates  that  even 
from  slight  winds  there  is  a  material  benefit  to  be  gained  when 
air  is  forced  with  little  pressure  into  the  under  drains.  In  none 
of  these  forced-air  plants  would  much  benefit  be  derived  unless 
the  filter  grains  be  quite  Coarse  and  the  pores  correspondingly 
large,  as  the  friction  opposed  to  the  air  by  fine-grain  sand  beds 
would  require  considerable  pressure  and  probably  result  in  the 
formation  of  blow  holes.  However,  actual  experiments  along  this 
line  are  too  few  to  permit  of  definite  conclusions;  except  that 
where  the  air  is  pumped  in  the  cost  of  operating  the  air  pump  or 
fan  is  too  great  in  proportion  to  the  benefit  derived;  also  the 
retarding  of  bacterial  action  when  the  air  introduced  has  a  low 
temperature  is  a  serious  objection. 

To  overcome  this  objection  of  low  temperature  Whittaker 
and  Bryant  in  1898  constructed  in  Accrington,  England,  a  "  thermal 
aerobic  filter,"  somewhat  similar  to  Ducat's  in  construction,  but 
in  which  jets  of  steam  sprayed  into  the  sewage  raised  the  tem- 
perature in  both  summer  and  winter  to  that  most  favorable  to 
bacterial  action. 

The  success  obtained  with  the  use  of  mechanical  filters  in  the 
purification  of  river  water  quite  high  in  sediment  has  led  to  the 
suggestion  of  their  use  for  purifying  sewage,  or  at  least  the 
effluents  from  tank  processes.  The  only  actual  experiments  along 
this  line  which  are  known  of  are  those  conducted  by  the  Massa- 
chusetts State  Board  of  Health  in  1906  and  1907.  The  effluents 


METHODS    OF    TREATMENT.  477 

from  six  experimental  trickling  filters  were  treated  with  copperas 
and  lime  in  varying  amounts,  also  with  sulphate  of  alumina, 
sugar  sulphate  of  iron  (a  new  form  of  ferrous  sulphate),  and 
some  other  substances.  "The  experiments  indicated  clearly  that 
satisfactory  removal  of  color,  turbidity,  and  a  considerable  pro- 
portion of  the  organic  matter  may  be  accomplished  by  coagulation 
with  sulphate  of  alumina,  or  with  one  of  the  three  forms  of 
ferrous  sulphate  mentioned,  combined  with  lime,  this  to  be 
followed  by  filtration  at  rates  of  25  million  gallons  per  day  or 
somewhat  higher  in  filters  of  the  mechanical  type.  The  removal 
of  from  90  to  99  per  cent  of  the  bacteria  occurred  only  when 
the  removal  of  suspended  matter  was  practically  complete.  The 
cost  of  coagulants  necessary  to  produce  an  effluent  free  from 
suspended  matter  was  so  large  when  iron  salt  and  lime  were  used 
and  the  volume  of  water  filtered  between  washings  was  so  small 
as  to  make  the  process  apparently  impracticable.  The  results 
obtained  during  the  early  portion  of  the  experiments  indicated, 
however,  that  clarification  might  be  produced  at  less  cost  with 
sulphate  of  alumina  than  with  either  of  the  iron  salts  tested, 
for  the  reason  that  much  larger  amounts  of  the  cheaper  iron 
salts  must  be  used;  they  require,  furthermore,  the  addition  of 
lime." 

Some  modifications  of  the  ordinary  sedimentation-tanks  other 
than  the  Dortmund  tanks  have  been  designed  from  time  to  time, 
but  we  believe  none  of  these  have  come  into  general  use  other 
than  those  already  referred  to.  One  of  the  most  promising  of 
the  new  inventions  removes  the  effluent  not  through  an  orifice 
or  weir  at  the  end,  but  by  placing  across  the  tank  at  close  intervals 
a  series  of  parallel  troughs  whose  edges  are  all  at  the  same  level 
and  which  connect  with  the  outlet  channel.  The  sewage  thus, 
instead  of  all  flowing  over  one  weir,  flows  over  the  edges  of  these 
troughs,  each  edge  of  which  has  a  length  equal  to  the  entire 
width  of  the  tank.  This  produces  a  very  gradual  motion  of  the 
sewage  distributed  uniformly  over  the  entire  tank.  This,  of 


478  SEWERAGE. 

course,  could  not  be  used  for  retaining  any  scum  or  floating 
material,  but  would  only  serve  for  retaining  the  sediment  or 
sludge. 

One  or  two  small  plants  in  Germany  have  used  a  clarification 
tank  which  is  placed  above  the  level  of  the  sewer,  the  sewage 
being  raised  into  it  by  the  siphoning  action  of  the  departing 
sewage  leaving  it  on  its  way  to  the  outlet.  The  necessity  for 
having  the  tank  absolutely  water  tight  and  the  other  expenses  of 
construction  would,  it  would  appear,  more  than  compensate  for 
the  saving  in  not  having  to  excavate  for  the  tank  in  order  to 
place  it  under  ground  where  the  flow  could  be  by  gravity.  This 
style  of  tank  is  known  as  the  Kessel. 


ART.  100.    DISPOSAL  OF  SLUDGE. 

It  is  shown  in  the  preceding  articles  that  all  tank  methods  of 
treatment,  and  other  treatment  which  is  not  preceded  by  a  pretty 
thorough  removal  of  suspended  matter,  produces  a  sludge  or 
other  accumulation  of  organic  matter.  In  fine-sand  filters  most 
of  this  is  strained  out  upon  the  surface  or  within  the  top  inch  or 
two.  In  coarse-grain  filters  it  collects  within  the  body  of  the 
filter,  but  is  generally  so  modified  as  to  lose  a  large  part  of  its 
putrescibility.  This  suspended  matter  offers  really  the  most  serious 
problem  connected  with  sewage  disposal,  and  one  to  which  no 
satisfactory  solution  has  yet  been  found. 

The  sludge  from  precipitation  tanks  is  merely  concentrated 
sewage  matter  which  has  undergone  little  change.  That  from 
septic  tanks  has  been  worked  over  by  bacteria  to  a  considerable 
extent  and  a  large  part  of  the  more  putrescible  matter  has  been 
liquefied  and  discharged  with  the  effluent;  so  that  the  remaining 
matter  is  high  in  carbons  and  in  the  more  resistant  nitrogenous 
matter.  It  is  therefore  less  offensive  and  more  easily  disposed 
of.  Moreover,  a  large  proportion  of  the  pathogenic  bacteria  have 
died  out.  The  matter  strained  out  by  fine-grain  sand  filters  is 


METHODS 


TREATMENT. 


479 


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480  SEWERAGE. 

generally  in  a  fairly  dry  state  and  frequently  contains  con- 
siderable quantities  of  fibrous  matter  such  as  cloth,  paper,  wood 
fibers,  etc. ;  and  this  matter  forms  a  thin,  more  or  less  continuous 
sheet  over  the  filter,  frequently  resembling  a  felt  or  paper  mache. 
This  matter  can  be  removed  easily  with  rakes  or  spades,  but 
putrefies  readily  if  again  subjected  to  moisture.  The  solid 
matters  from  sprinkling  filters,  and  to  a  less  extent  from  contact 
filters,  have  been  so  modified  as  to  have  lost  considerable  of  their 
tendency  to  putrefy,  and  are  considerably  more  stable  than 
septic  effluent. 

There  is  manurial  matter  of  value  in  the  sludge  of  precipitation- 
tanks  and  to  a  less  extent  in  other  sludges,  but  no  process  has  yet 
been  found  by  which  its  value  can  be  utilized  at  a  profit.  One  of 
the  difficulties  is  that  sludge,  although  concentrated  sewage,  still 
contains  a  very  large  percentage  of  water.  Glasgow  sludge  was 
found  to  contain  4.63  per  cent  of  organic  matter,  5.60  per  cent  of 
mineral  matter,  and  89.77  Per  cent  °f  water.  Septic  sludge  con- 
tains somewhat  less  water  and  also  yields  up  its  water  content 
more  readily.  The  addition  of  lime  to  sludge  to  "cut  the  slime" 
permits  the  more  ready  exclusion  of  water.  Table  No.  29  gives 
the  analyses  of  English  sludges  as  found  by  Dr.  Wallace,  these 
sludges  having  been  dried  in  air  to  a  degree  which  could  be 
obtained  only  by  long  exposure  to  sunlight.  This  table  shows 
the  value  of  various  sludges  from  chemical  precipitation  to  vary 
from  about  $2.50  to  about  $8.00  per  ton.  These  values,  however, 
do  not  take  into  account  any  neutralizing  effect  of  other  con- 
stituents, or  qualities  which  makes  its  use  less  desirable  than  that 
of  other  fertilizers.  As  a  matter  of  fact  no  method  has  yet  been 
found  by  which  the  fertilizing  values  of  sludge  can  be  made  use 
of  to  sufficient  advantage  to  induce  farmers  to  use  it  even  when 
it  is  given  them  free  of  cost,  except  in  a  few  cases. 

London  maintains  a  number  of  sludge  ships,  each  carrying 
looo  tens,  which  each  day  carry  more  than  300  million  gallons 
of  sludge  50  miles  to  sea  and  dump  it  there.  Some  cities  dis- 


METHODS  OF   TREATMENT.  481 

charge  septic  sludge  into  rivers  during  high  water,  Columbus 
finding  that  a  dilution  of  800  volumes  of  water  to  one  of  sludge 
prevents  a  nuisance.  Probably  the  most  common  method  of 
disposal,  however,  is  to  drain  the  sludge  off  onto  sludge  beds, 
these  being  beds  of  sand  or  other  porous  soil,  of  ashes  or  other 
porous  artificial  material,  the  bed  being  surrounded  by  a  low 
bank  for  retaining  the  liquid  sludge.  Here  the  water  is  allowed 
to  drain  away  and  the  solid  material  when  comparatively  dry  is 
raked  up  and  either  burned,  used  for  filling  in  low  lands,  buried 
in  pits  and  covered  over  with  soil,  or  in  some  cases  has  been  used 
as  fertilizer.  The  drying  sludge,  especially  when  from  plain 
precipitation,  may  give  off  considerable  odor,  and  in  some  cases 
a  better  plan  has  been  found  to  be  to  furrow  the  land  quite  deeply, 
run  the  sludge  into  these  deep  furrows,  and  return  the  earth  to 
the  furrows  as  soon  as  the  sludge  has  partially  drained.  Much 
of  the  odor  may  be  avoided  by  sprinkling  chloride  of  lime  over 
the  drying  sludge. 

The  quantity  of  sludge  which  would  accumulate  from  a  large 
plant  is  enormous,  and  the  amount  of  land  which  would  be 
required  for  sludge  beds  is  considerable,  since  each  bed,  after  an 
application  of  sludge,  requires  a  long  rest  for  thorough  drainage 
and  oxidation  of  the  organic  matter  which  was  carried  into  it 
during  the  drainage  of  the  sludge.  Instead  of  sludge  beds  for 
removing  the  water,  filter  presses  are  used  in  a  number  of  cases, 
especially  in  connection  with  chemical  precipitation.  The  filter 
press  is  composed  of  a  number  of  circular  or  square  iron  plates, 
each  face  of  which  is  grooved  and  recessed,  which  rest  vertically 
face  to  face  in  a  simple  frame  and  slide  away  from  each  ether  on 
horizontal  guides.  Between  each  two  plates  is  a  canvas  bag. 
Through  these  plates  passes  a  central  feed  passage  through  which 
the  sludge  is  forced  into  the  canvas-lined  cells  thus  formed,  the 
water  being  expelled  through  the  canvas  by  a  pressure  in  the  feed- 
pipe of  about  100  pounds  per  square  inch.  It  is  seen  that  this  is 
really  a  method  of  extracting  the  water  by  forcing  it  out  through 


482  SEWERAGE. 

a  canvas  bag  which  retains  the  suspended  matter  within  it.  By 
this  method  the  amount  of  contained  water  is  reduced  from  90 
to  95  per  cent  to  from  45  to  65  per  cent.  The  cakes  thus  formed 
are  sufficiently  solid  to  be  handled,  although  when  dumped  into 
cars  or  otherwise  treated  in  bulk  they  generally  break  into  masses 
of  several  cubic  inches  each.  In  Worcester  the  cakes  thus  formed 
are  36  inches  in  diameter  and  2  inches  thick.  They  give  off  little 
odor  and  will  burn  in  a  crematory  without  other  fuel.  In  most 
cities  of  this  country  the  cakes  are  dumped  on  low  land,  where 
they  undergo  more  or  less  slow  putrefaction,  but  give  little  offense. 
The  fluid  forced  out  by  the  press  is  very  foul  and  is  generally 
removed  to  the  sewer  for  treatment  with  the  crude  sewage. 

There  are  few  figures  showing  the  cost  of  pressing  sludge  into 
cakes  separate  from  the  other  costs  connected  with  chemical 
disposal.  Such  as  there  are  seem  to  indicate  that  the  cost  of  press- 
ing is  about  50  to  75  cents  per  ton  of  cake  containing  50  per  cent 
moisture. 

In  a  report  published  in  1908  by  the  Ohio  State  Board  of 
Health,  the  disposal  of  septic  sludge  in  that  state  is  described, 
and  may  be  summarized  as  follows:  The  removal  and  disposal 
of  well-digested' sludge  from  a  septic  tank  is  not  an  objectionable 
undertaking  and  does  not  possess  so  many  disagreeable  features 
as  might  at  first  be  supposed.  Provided  sufficient  time  is  allowed 
for  a  partial  digestion  of  the  sludge,  there  appears  to  be  no  par- 
ticular difficulty  or  odor  connected  with  the  operation.  The 
sludge  is  inky  black  in  color,  homogeneous,  and  granular,  and 
when  allowed  to  dry  oxidizes  rapidly  and  takes  a  form,  closely 
allied  to  humus  matter.  In  some  plants  it  is  pumped  by  a  cen- 
trifugal or  dredge  pump;  in  others  it  is  thicker  and  is  shoveled 
into  buckets.  Where  it  is  thinnest  a  contractor's  diaphragm 
pump  has  been  used  for  raising  it  from  the  tank.  There  is 
usually  a  considerable  saving  in  expense  if  a  sludge  drain  is 
provided  for  draining  it  off  by  gravity  onto  a  sludge  bed;  but 
in  some  cases  there  is  no  ground  sufficiently  low  available  for 


METHODS  OF   TREATMENT.  483 

this  purpose.  At  one  plant  the  mixed  sludge  and  supernatant 
sewage  is  removed  by  a  steam  siphon  comprising  a  one-half  inch 
steam  pipe  and  four-inch  discharge  pipe.  At  Shelby,  Ohio,  a 
plant  is  used  which  is  considered  very  satisfactory  for  small  plants. 
It  comprises  a  bucket  conveyor  which  is  placed  over  the  tank 
on  a  platform  erected  for  that  purpose,  by  which  the  sludge  is 
raised  by  hand  power  and  discharged  through  a  trough  into  a 
tank  wagon  from  which  it  is  sprinkled  onto  the  surface  of  grassed 
land.  The  entire  contents  of  the  tank,  about  7700  gallons,  is 
previously  stirred  with  a  pole,  and  the  liquid  flows  readily  both 
into  and  from  the  wagon. 

The  amount  of  sludge  varies  considerably  in  the  different 
Ohio  plants,  largely  owing  to  the  differences  in  the  amount  of 
suspended  matter  which  is  carried  over  with  the  effluent.  It  is 
probable,  however,  that  the  amount  will  average  about  three  cubic 
yards  of  accumulated  sludge  per  million  gallons.  In  most  plants 
the  sludge  is  discharged  by  drain,  bucket,  or  otherwise  upon  beds 
of  coarse  sand,  fine  cinders,  coke  or  ashes.  It  seems  desirable 
to  underdrain  such  beds  so  that  the  liquid  portion  may  be  drained 
off  as  soon  as  possible  and  thus  hasten  the  oxidation  of  the  solid 
residue.  Where  the  sludge  required  to  be  removed  by  hand 
the  cost  in  the  Ohio  plants  was  found  to  be  about  50  cents  to 
$1.00  per  cubic  yard.  Where  regular  arrangements  are  made  for 
draining  it  off  or  otherwise  removing  it  by  special  fixed  appliances 
the  cost  in  large  plants  elsewhere  has  been  as  low  as  5  cents  per 
cubic  yard. 

In  practically  all  chemical  precipitation  plants,  where  machin- 
ery is  required  for  the  daily  processes,  pumps  are  provided  for 
removing  the  sludge,  which  is  drawn  off  into  a  suction  well  or 
sludge  pit  by  means  of  pipes  from  the  sedimentation  tanks  fur- 
nished with  valves  for  regulating  their  use. 

The  material  removed,  largely  by  screening,  from  the  sewage 
of  the  Metropolitan  system  of  Boston  before  pumping  is  com- 
pressed into  blocks  which  are  burned  as  fuel  under  the  boilers. 


484  SEWERAGE. 

This  was  found  to  burn  out  the  brickwork  very  rapidly  in  the 
externally-fired  boilers  but  to  have  no  effect  upon  the  steel  plates; 
in  consequence  of  which  internally-fired  Scotch  boilers  have  been 
adopted,  the  combustion-chambers  being  made  of  steel  plates 
with  water  spaces,  and  with  no  brickwork  except  in  the  bridge 
walls  and  around  the  fire  doors. 

The  amount  of  sludge  removed  by  the  various  processes  has 
been  referred  to  in  the  previous  articles.  Average  raw  sewage 
contains  about  200  parts  per  million  of  suspended  matter,  or,  say, 
one  cubic  yard  per  million  gallons,  and  double  this  of  compressed 
sludge  or  ten  to  twenty  times  that  amount  of  wet  sludge.  A  very 
large  percentage  of  this  remains  to  be  disopsed  of,  whatever  the 
treatment,  unless  it  be  carried  away  with  the  effluent.  In 
Worcester,  Mass.,  one  part  of  sludge  is  obtained  from  90  parts 
of  sewage,  there  being  one  ton  of  solid  matter  to  750,000  gallons 
of  sewage,  34  per  cent  of  this  being  organic  matter.  With  a  lime 
precipitant  there  would  be  about  0.4  of  a  pound  of  sludge  per 
capita  daily.  The  experiments  with  Columbus  sewage  gave  5.75 
cubic  yards  of  wet  sludge  (87  per  cent  water)  per  million  gallons 
removed  by  plain  sedimentation;  and  about  the  same  deposited 
in  septic  tanks,  which  was  reduced  to  2.68  cubic  yards  by  hydrolysis. 
By  chemical  precipitation  11.4  cubic  yards  of  sludge,  92  per  cent 
of  water,  was  obtained,  or  about  the  same  amount  of  solid  matter. 

ART.  101.    SUMMARY. 

The  methods  of  treatment  described  produce  effluents  differing 
widely  in  quality.  They  use  materials  of  construction  of  various 
kinds;  require  areas  some  many  times  larger  than  others.  Some 
involve  a  fall  or  loss  of  head  of  only  a  few  inches,  others  of  several 
feet.  Some  are  best  adapted  to  fresh  sewage,  some  to  stale,  and 
others  to  sewage  containing  large  amounts  of  trade  wastes. 
(Special  methods  are  required  in  many  instances  for  the  treatment 
of  trade  wastes,  especially  those  high  in  fats,  fibrous  or  other 


METHODS  OF  TREATMENT.  485 

carbonaceous  matter.)  Where  anything  approaching  complete 
purification  is  necessary  a  combination  of  two  or  even  three  methods 
is  generally  most  effective  and  economical.  Which  methods 
should  be  employed  can  be  properly  decided  only  after  a  careful 
study  of  the  conditions. 

For  a  high  degree  of  purification  only  one  practicable  method 
is  known — intermittent  sand  filtration.  For  high  bacterial 
purification,  either  intermittent  filtration  or  disinfection  may  be 
used.  For  producing  non-putrescible  effluents  the  sprinkling 
filter  seems  to  be  the  most  effective  and  economical  of  area, 
although  double  contact  filters  give  excellent  results  and  are 
probably  cheaper  in  construction. 

In  connection  with  any  of  the  above  except  intermittent 
filtration  some  preliminary  treatment  is  necessary  to  remove 
the  coarser  suspended  matter;  and  this  is  advisable  with  fine- 
grain  filters  also,  although  the  sand  which  composes  these  strains 
out  upon  the  surface  most  of  the  suspended  matter.  For  such 
preliminary  treatment  screens  followed  by  sedimentation  are 
generally  best.  The  sedimentation  tank  may  be  operated  as  a 
septic  tank,  by  which  the  sludge  is  considerably  reduced  in  volume, 
and  that  remaining  is  less  offensive  and  contains  much  fewer 
pathogenic  bacteria.  Fine-grain  filters  used  for  final  treatment, 
however,  seem  to  clog  up  more  rapidly  and  deeply  with  septic 
than  with  plain  sedimentation  effluent. 

The  structural  features  require  engineering  skill  combined 
with  knowledge  of  the  principles  of  the  physical  and  bacterial 
actions  taking  place.  The  best  arrangement  of  the  several  parts 
will  usually  be  determined  to  some  extent  by  the  topography  of 
the  site.  The  fact  that  the  preliminary  processes  require  less 
area  than  the  final  has  suggested  a  general  circular  form,  the 
sewage  progressing  radially  from  the  center  outward  through 
concentric  tanks  or  beds;  but  in  most  cases  the  sewage  advances  in 
parallel  lines  from  one  end  of  the  plant  to  the  other. 

The  matter  of  applying  the  sewage  to  filters  is  a  detail  which 


486 


SEWERAGE. 


METHODS  OF  TREATMENT.  487 

varies  in  different  plants.  In  the  case  of  sprinkling  niters,  pipes 
are  generally  laid  along  the  bottom,  with  a  riser  to  carry  each 
nozzle  coming  vertically  from  tees.  The  pipes  should  be  arranged 
in  straight  lines  with  removable  plugs  at  each  end  so  that  they 
can  be  cleaned  out  if  necessary. 

Contact  beds  ordinarily  require  no  special  arrangements  for 
distributing  the  sewage;  but  fine-grain  filters,  if  filled  by  a  slow 
stream  from  one  point  only,  would  be  apt  to  pass  most  of  the 
sewage  through  the  bed  near  that  point.  For  this  reason  distrib- 
utors, generally  in  the  form  of  troughs,  are  laid  across  the  bed. 
Wooden  troughs  are  most  common,  and  last  four  or  five  years. 
Split  sewer  pipe  are  used,  also.  These  must  be  laid  practically 
level  so  that  the  sewage  will  flow  over  their  edges  for  their  entire 
length.  These  troughs  sometimes  radiate  from  the  inlet,  or  may 
be  parallel  and  provided  with  branches  so  as  to  reach  all  parts 
of  the  bed,  the  troughs  being  spaced  10  to  25  feet  apart. 

Where  the  sewage  is  flushed  on  in  doses,  distributors  are  not 
often  necessary,  but  a  slab  or  apron  is  placed  extending  for  2  to  5 
feet  around  the  outlet  to  prevent  wash.  Dosing  devices  of  various 
kinds  have  been  used,  perhaps  the  most  common  being  siphons 
similar  in  action  to  automatic  flush  tanks.  Also  various  ar- 
rangements of  tipping  tanks  are  used,  air  compressed  by  the 
rising  sewage,  and  other  contrivances  for  alternating  the  flow 
from  one  bed  to  another.  Generally  a  dosing  tank  or  chamber 
is  provided  which,  as  it  fills  each  time,  is  discharged  to  different 
beds  in  succession.  These  necessarily  involve  a  loss  of  head 
equal  to  the  depth  of  the  dosing  tank. 

Constant-flow  tanks  involve  a  loss  of  head  of  only  an  inch 
or  two;  intermittent  flow,  the  depth  of  the  tank.  All  filters 
require  a  loss  of  head  equal  to  their  depth,  which  should  generally 
be  at  least  four  or  five  feet.  Sludge  beds  must  be  lower  than 
the  bottoms  of  the  tanks  if  the  sludge  is  to  be  drawn  out  by 
gravity. 

Sewage  treatment  plants  need  not  be  particularly  offensive 


488  SEWERAGE. 

in  any  feature  except  the  sludge  disposal,  but  this  can  hardly 
help  but  offend  the  senses.  Fine-grain  niters,  however,  if  in- 
telligently operated,  create  only  dry  sludge  which  can  be  burned 
or  otherwise  disposed  of  inoffensively;  and  many  of  these  are 
operated  near  residences  without  creating  a  nuisance.  But  in 
general  it  will  be  necessary  to  arrange  for  the  treatment  and 
disposal  of  wet  sludge  at  a  distance  from  any  built-up  section. 
In  most  cases  such  a  location  would  be  chosen  in  any  event, 
because  of  the  necessity  for  obtaining  cheap  land,  since  con- 
siderable areas  are  required. 

The  cost  of  nitration  plants  cannot  be  estimated  very  closely 
without  definite  knowledge  of  the  amount  of  grading  necessary, 
and  of  the  local  cost  of  sand,  gravel,  broken  stone,  coke  and  similar 
materials.  Each  acre  of  filter  five  feet  deep  contains  8,067  cubic 
yards  of  filter  material,  and  this  has  in  most  plants  cost  from 
$i  to  $2  in  place.  In  a  considerable  number  of  plants  fine  sand 
filters  are  made  by  stripping  the  top  soil  from  natural  sand  beds 
and  placing  under-drains  by  trenching.  In  coarse-grain  filters, 
however,  this  is  not  possible;  unless  a  bed  of  coarse  and  perfectly 
clean  gravel  be  available  for  a  sprinkling  filter — a  formation  which 
is  very  rare.  The  distributing  pipes  and  nozzles  for  10  acres  of 
sprinkling  filter  at  Columbus,  O.,  cost  $27,700,  and  the  filtering 
material  in  place  (80,120  cubic  yards)  cost  $125,800.  Six  septic 
tanks  in  the  same  plant  having  a  combined  capacity  of  8,020,000 
gallons  cost  $66,730,  of  which  $48,070  was  for  reinforced  concrete, 
$12,530  for  sluice  gates,  and  the  balance  for  earth  work,  scum 
boards  and  miscellaneous.  The  total  cost  of  septic  tanks,  sprink- 
ling filters  and  settling  basins,  with  gate  house,  piping  and  all 
appurtenances,  for  purifying  20,000,000  gallons  in  24  hours  cost 
$456,350,  or  $22,820  per  million  gallons  per  day.  The  following 
table,  compiled  from  data  collected  by  the  Ohio  State  Board  of 
Health,  gives  the  cost  and  other  data  of  the  plants  of  that  State. 


METHODS   OF    TREATMENT 


489 


TABLE  No.  30. 

DESCRIPTION   AND    COST    OF    MUNICIPAL   PURIFICATION    PLANTS    IN    OHIO. 
(From  Report  of  Ohio  State  Board  of  Health,  1908.) 


Population 

Rate  of  Sewage  Flow, 
Gallons  per  24  hours. 

Preparatory  Treatment. 

Tank  Treatment. 

Place. 

Total. 

Trib- 
utary 
to 
Sewers 

Average. 

Maximum. 

Screen- 
ing. 

Grit 
Cham- 
bers. 
Capacity, 
Gallons. 

Kind. 

Capacity, 
Gallons. 

Alliance  

14,000 

6,500 

1,600,000 

2,170,000 

Iron 
bars. 

Chem- 
ical. 

120,000 

Ashland  .... 

7>5oo 

3,000 

340,000 

1,000,000 

3,780 

Septic. 

39.OOO 

Canton  

50,000 

23,500 

2,500,000 

3,100,000 

Iron 

Chem- 

strips. 

ical. 

700,OOO 

Clyde  

2,800 

I   O  ^O 

172  ooo 

360  ooo 

Sludge 

1  »UOV 

boxes. 

Columbus  .  .  . 

190,000 

12,670,000 

21,400,000 

Cage 

Septic 

and 

tanks. 

8,020,000 

vertical. 

Delaware  .  .  . 

10,000 

4,000 

433,000 

1,000,000 

Iron 

3.300 

Septic. 

IOO.OOO 

bars. 

E.  Cleveland  . 

8,000 

7,000 

365,000 

2,000,000 

None. 

64,000 

Septic. 

170,000 

Fostoria  

10,000 

5,000 

277,000 

489,000 

Iron 

None. 

None. 

strips. 

Geneva  

2,500 

1,200 

181,000 

450,000 

None. 

7.5oo 

Septic. 

39,000 

Glenville.  .  .  . 

9,000 

6,500 

1,200,000 

3,000,000 

Iron 

None. 

Chem- 

strips. 

ical. 

184,000 

Kenton  

400 

400 

18,000 

260,000 

None. 

None. 

Septic. 

18,800 

Lakewood.  .  . 

10,000 

7,000 

500,000 

3,540,000 

None. 

None. 

Septic. 

300,000 

London  

4,000 

500 

50,000 

None. 

3  ,500 

Septic. 

3  4.  7OO 

Mansfield  .  .  . 

24,000 

12,000 

1,000,000 

3,000,000 

W.  I. 

6,000 

Septic. 

1,000,000 

bars. 

Marion  

19,000 

8,000 

650,000 

2,000,000 

None. 

19.300 

Septic. 

414,000 

Oberlin  

5,200 

3.400 

250,000 

1,000,000 

None. 

None. 

Sludge 

pits. 

6,700 

j-Septic. 

12,500 

Plain  City.  .  . 

1,  800 

725 

175,000 

720,000 

None. 

None. 

I  Sludge 

I  pits.  .  . 

7,700 

Shelby  

6,000 

i,  600 

238,000 

1,000,000 

None. 

None. 

Reser- 

1,660,000 

voirs. 

Westerville.  . 

1,500 

300 

36,000 

200,000 

None. 

None. 

Septic. 

22,000 

Xenia  

10,000 

375,000 

None. 

None. 

Sludge 

pits. 

9,500 

49° 


SEWERAGE. 
TABLE  No.  30— Continued. 


Place. 

Purification  Devices. 

X  O 
§<0 

ill 

H'55  E 

w  3  3 

i!l 

$22,000 

*5,ooo 

26,545 

1,000 

456,350 

12,000 

23,092 

f2I,30O 

13,500 

10,000 

4,000 

24,175 

15,000 

35,720 

43,000 

990 
•(•19,000 
4,000 
2,900 
6,000 

If 

JL 
!>s« 

o 
$3,600 

3-375 
135 

Noth- 
ing.! 

1,000 

700 

3,ooo 
in 
250 

Noth- 
ing. J 
2,750 
1,125 

500 
190 
700 
Small. 

Primary. 

Secondary. 

Kind. 

Filtering  Material. 

||| 

Filtering  Material. 

Kind. 

d 

i~ 

26 

| 

Kind. 

V 

rCf"53 

!~ 

|J 

Alliance  

Sand. 

Sandy 
gravel. 

4-99 

600 

None. 

Clyde  

Sand. 

Sprink 
ling 
filters. 
Contact. 

Strain- 
ers. 

Sand, 
sand 
trenches 
and 
land. 
Sand. 

Strain- 
ers. 
Strain- 
ers. 
Contact. 

Contact 

Contact. 
Contact. 

Land. 
Contact 
Cinders. 
Contact 
Gravel. 

Clayey, 
sand. 
Broken 
stone. 

Coke. 
Slag. 

Sand 
and 
clay 
soil. 

Sand 
and 
gravel. 
Gravel, 
coke. 
Stone. 

Gravel, 
cinders. 
Coke. 

Cinders. 
Stone. 

Loam. 
Cinders. 
Cinders. 
Coke. 
Gravel. 

48 
64 

36 
30 

36 

48 
36 

24 

60 

36 

57 
33 

36 
36 
18 
36 
36 

2.70 
10 

0.66 
0.168 

20 

0.62 
0.372 

390 
19,000 

6,000 
42,000 

250 

1,940 
17,500 

None. 

Settling 
basins. 

None. 

Sand, 
coke, 
broken 
stone. 

None. 

52 

3 

Columbus  

Delaware  
E.  Cleveland  .... 

60  to 
66 

0.248 

Geneva  
Glenville  

None. 

Sand. 

Coke, 

stone. 
None. 

None. 

None. 
Sand 
and 
fine 
stone. 
None. 
None. 
None. 
Cinders. 
None. 

36 

6  to 
24 

36 
72 

i  .0 
0.069 

0.55 

0.022 

Lakewood  
London  

0.625 
0.25 

1-25 
0-55 

5-25 

0.07 
0.57 
o.  126 
1.47 

11,200 
2.OOO 

9,6OO 
14,500 

650 
10,400 
2,800 
2,400 

Mansfield  
Marion  

Oberlin  
Plain  City  
Shelby 

Westerville  
Xenia  

*  Including  cost  of  land.  t  Includes  sewerage  system. 

J  Attention  of  regular  sewer  superintendent  not  charged. 


METHODS   OF    TREATMENT. 
TABLE  No.  31. 

PARTIAL    LIST    OF    SEWAGE-TREATMENT    PLANTS    IN    THE 
UNITED    STATES. 


491 


Intermittent  Filtration.* 

Broad  Irrigation,  Sewage  Farming  or  other 
Land  Disposal. 

Town  or  City. 

Population. 

Town  or  City. 

Population. 

2  Toledo,  O        

190,000 
138,000 
83,000 
60,000 

55>°°° 
50,000 
40,000 

35  >°°° 
33,000 
29,000 
24,000 
24,000 
18,000 
15,000 
15,000 
15,000 
13,000 

12,000 
12,000 
11,302 
10,500 
10,000 
10,000 

9>5°° 
9,000 
9,000 
8,000 

7,5°° 
6,800 
6,300 
6,000 
6,000 
6,000 
6,000 
5,200 
5,200 
5,000 

3>5°° 
2,800 
2,500 

San  Antonio,  Tex  

85,000 
45,000 
21,000 
20,500 

20,000 
20,000 
17,000 
15,000 
12,800 
I2,OOO 
II,50O 
11,302 
IO,20O 
10,200 
9,OOO 
8,200 
7,OOO 

7,000 
7,000 
6,700 

6,200 

6,100 
5,100 
5,000 
5,000 
5,000 
4,800 
4,668 
3,000 

1  Worcester,  Mass  
Houston,  Tex  

Colorado  Springs,  Col  
Helena,  Mont  

2  Altoona,  Pa  

Walla  Walla,  Wash  

Brockton,  Mass  

Pasedena,  Cal  

5  Pawtucket,  R.  I  

New  Britain    Conn 

Phoenix,  Ariz  

Tuscon   Ariz 

Woon  socket   R   I 

Sherman    Tex 

M^eriden    Conn 

Hastings   Neb 

Pittsfield    Mass 

1  Santa  Rosa   Cal 

Central  Falls   R    I 

**  Pomona    Cal 

Danbury    Conn. 

*  Framingham    M^ass 

Marinette    Wis  

Fostoria    O 

Clinton,  Mass  

Redlands    Cal 

Marlboro,  Mass  

La  ramie    Wyo 

Paris,  Tex  

Columbia    Mo  .         

Gardner,  Mass  

Bakersfield,  Cal  

Manchester   Conn 

McKinney,  Tex  
Princeton    N    J 

South  bridge   M^ass 

Framingham   Miass 

York   Neb 

1  Xenia    O 

Greeley    Col 

Natick   M^ass 

Brookfield   Mo 

Bristol    Conn  . 

Raton,  N.  M  
St    Johns   Mich 

Burlington,  N.  J  
6  Waukesha,  Wis  

Visalia   Cal 

1  Glenville,  O  

Elkins   W   Va 

Spencer,  Mass  

Milford    Del 

5  Ashland,  O  

Red  Jacket   Mich 

Andover,  Mass  

North  Brookfield,  Mass.  .  . 

Vineland,  N.  J  

Concord    Mass 

West  bo  ro    Mass 

Franklin    M^ass 

5  Princeton    111 

Ripon    Wis 

Mendota    111 

Aiken   S.  C 

Leicester   Mass  . 

Clyde,  O     , 

5  Geneva,  O  

Soldiers'  Home,  Wis  

1  Also  chemical  precipitation. 

2  Part  of  the  sewage  only. 


4  Also  intermittent  filtration. 

5  Also  septic  tank. 


492 


SEWERAGE. 


TABLE  No.  31 — Continued. 


Town  or  City. 

Population 

Town  or  City. 

Population. 

CHEMICAL  PRECIPITATION. 
Providence,  R.  I  

210,000 

SEPTIC  TANKS  —  Cont'd. 
2  Pomona,  Cal  

II   COO 

1  Worcester,  Mass.  . 

I  ^8  OOO 

*  Independence   Mx> 

26th  Ward,  Brooklyn.  . 

Urbana,  111 

Canton,  O  

50  ooo 

7  Holland    Mich 

New  Rochelle,  N.  Y.  .  . 

24,000 

DeKalb,  111... 

IO  OOO 

White  Plains,  N.  Y.... 

15,000 

6  Lakewood,  O  

IO  OOO 

Alliance,  O 

14  ooo 

6  Delaware    O 

Anaconda,  Mont  .... 

I  3  OOO 

8  Bloomingjton    Ind 

2  Santa  Rosa,  Cal  

I  2  OOO 

Aberdeen    S    D 

O  800 

3Glenville,  O  

O  OOO 

8  Kenton    O 

1  Waukesha,  Wis.  . 

y»juu 
o  ooo 

SEDIMENTATION. 
1  Central  Falls,  R.  I.  . 

24  ooo 

Rutherford,  N.  J  
Ashland    O 

8,500 
8  ooo 

Leadville,  Col  
Paris,  111  

^S00 

I  2  IOO 

8E.  Cleveland,  O  
8  Hanover   Pa 

8,000 

Boulder,  Col  .       ... 

12  OOO 

2  Elberton    Ga 

OutJ 

Trinidad,  Col  

IO  OOO 

Centerville    la 

Amherst,  Mass  

6  ooo 

M^acomb   111 

8  Shelby,  O  

6  ooo 

1  Marshfield    Wis 

7  ooo 

N.  Milwaukee,  Wis.  .  .  . 
West  Salem,  Wis  

2,000 

1,000 

1  Andover,  Mass  
6  Red  Bank   N    J 

6,800 

6  coo 

SEPTIC  TANKS. 

6  Danville,  Ky  
1  Princeton,  111  

6,500 
6  ooo 

5  Seattle,  Wash  

27?  COO 

1  Oelwein   la 

8  Columbus   O 

1  80  ooo 

Highland  Park   111 

1  Omaha,  Neb  

ICO  OOO 

San  Luis  Obispo   Cal 

5  coo 

4  *  5  Worcester,  Mass  

138  ooo 

1  Monroe,  Wis 

54.00 

100,000 

6  Marion,  la 

53OO 

8  Reading    Pa 

gc  OOO 

Wilmington    Kan 

5  Little  Rock  Ark 

60  7OO 

6  Oberlin   O 

j>jw 

1  Pawtucket,  R.  I  

50,000 

LaGrange,  111  

c,ooo 

8  Allentown,  Pa  
6  Charlotte,  N.  C. 

50,000 

4C  OOO 

6  Lancaster,  N.  Y  
1  Wagoner    Okla 

4,800 

4  COO 

Bellingham,  Wash..     . 

38  coo 

Tomah   Wis 

4  3OO 

58  Kingston,  N.  Y  

3  2,000 

1  Liberty,  N.  Y. 

4  OOO 

8  Jackson,  Mich  

32,000 

Depew,  N.  Y  

4  ooo 

1  Madison,  Wis  

26,000 

6  London,  O  

4  ooo 

6  Plainfield    N    J 

2C  OOO 

1  Geneva    O 

•7  000 

6  Mansfield,  O  . 

24  OOO 

\Vauwatosa    \Vis 

•j   2OO 

6  Fond  du  Lac,  Wis     . 

22  OOO 

1  Lancaster   Wis 

-?  ooo 

1  6  Marion,  O  

I9,OOO 

Lake  Forest    111. 

T,  OOO 

2  Hot  Springs,  Ark  
Ithaca,  N.  Y  

17,700 
l6,OOO 

Hopedale,  Mass  
Verona,  N.  J  

2,200 
2,2OO 

Salisbury   N   C 

1C  OOO 

Elkhorn    Wis 

2  OOO 

8  Marshalltown   la 

jc  OOO 

8  Plain  City    O 

I  800 

Champaign,  111.. 

i<5  ooo 

8  6  Westerville    O 

I   COO 

Kewanee,  111  

15  ooo 

1  Milwaukee    County   In- 

8 Olean   N   Y 

stitutions 

Paris  111 

12  IOO 

Glen  View   111 

1  Also  intermittent  filtration. 

2  Also  broad  irrigation. 

3  Also  coke  and  sand  filters. 

4  Also  chemical  precipitation. 

5  Part  of  the  sewage  only. 


6  Also  contact  beds. 

7  Also  coke  strainer. 

8  Also  continuous  filters. 

9  Also  sprinkling  filters. 


INDEX. 


PAGE 

Acceptance  of  a  system,  Requirements  for 209 

Adams  Sewage-lift •. 136 

Advertising  contracts 235 

Aeration  of  niters 433,  475 

Air,  sewer,  Character  of 80,  83 

Albuminoid  ammonia,  Definition  of 376 

Alignment,  Giving  trench 240 

Alleys,  Sewers  in 102 

Ammonia,  Formation  of,  in  sewage 376,  431 

Analyses,  Chemical 375 

Angles  and  bends  in  sewers 56,  103 

Arches,  Providing  for  thrust  of 294,  306 

Assessments,  Conditions  governing 229,  232 

,  Methods  of  making 227 

Atlantic  City,  Gaugings  of  sewage  flow  at 23 

Back-filling,  Cost  of  tamping 205 

' '         ,  Laborers  used  for 264 

,  Specifications  for 205 

Bacteria  in  sewage,  Effect  of 374,  386,  429 

Barrel,  sewer,  Shape  of 65,  142 

Beginning  construction,  Points  for 237 

Bends  in  sewer  lines 56,  103 

Benefits  derived  from  sewerage i,  2,  123,  232 

Berlier  system  of  sewerage 7 

Bids,  Receiving  and  considering 235 

Blacksmith,  Necessity  for,  during  construction 262 

Borings,  Test,  along  sewer  lines 93 

Boulders,  Removing,  from  trench 270 

Braces,  Extensible 283 

' '     ,  Measuring  trench  for 283 

Branches,  Laying  sewer 202,  238,  247,  292,  339 

Bricks  for  sewers,  Cost  of 221 

,  Specifications  for 182 

Brick  sewers,  Abrasion  of 61 

'  *          ,  Centre  for 296 

,  Cost  of  construction 226 

493 


494  INDEX. 

PAGE 

Brick  sewers  in  quicksand 320 

,  Invert  backing  for * 293,  300 

,  Method  of  building 295,  314 

,  Templet  for 244,  294 

Bridging  trenches,  Specifications  for 189 

Broad  irrigation,  Cost  of 445 

,  Crops  grown  by 438 

,  Definition  of 435 

,  Methods  used  in 436 

Broken  stone,  Specifications  for 185 

Burlington,  Vt.,  Gaugings  of  sewage  flow  at 24 

C,  Effect  of  variations  in  R  upon 46,  55 

"  ,  Meaning  of  45 

"  ,  value  of,  Formulas  for  the 46 

Canals,  Crossing  under 335 

Capacity,  Designing  for  future 97 

Catch-basins,  Cleaning 131,  346,  352 

' '          ,  Construction  of 168 

' '          ,  Where  to  use 130,  346 

Caving  of  banks,  Avoiding 269,  274 

Cement,  Cost  of 227 

' '       pipe-joints,  Cost  of 223 

' '       sewer-pipe,  Use  of 142,  156 

,  Specifications  for 181 

' '      ,  Specifications  for 185 

Centre  for  brick  and  concrete  sewers 298,  302 

Cesspools 3 

Chemical  analyses 375 

"         precipitation.     See  Precipitation. 

Chemistry  of  sewage 373>  37^ 

Chezy  formula 45 

Chlorine  as  a  disinfectant 468 

Chlorine  in  sewage 369>  373>  377 

Circular  sewers,  Conditions  favoring  use  of 65 

Clarification,  Definition  of 4°3 

Cleaning  large  sewers 354>  35^ 

*  *        sewers,  Cost  of 358 

"        small  sewers 260,  324,  353 

c '        up  streets,  Specifications  for 209 

Coffer-dams,  Construction  of 33° 

Combined  system  defined - 9 

'  *  vs.  separate 10 

Composition  of  sewage 367>  379 

Concrete  sewers J47 

"  ,  Method  of  constructing 300 

"  ,  Specifications  for 192,  i98 

"  ,  Thickness  of r 225 


INDEX.  495 

PAGB 

Consumption  of  water,  Daily  and  hourly  variation  in 16 

,  Estimating  future 16 

,  per  capita,  Table  of , .. ;     15 

Contact  filters,  Operation  of 452 

,  Results  obtained  by 450 

,  Theory  of  operation  of 448 

Contract,  Form  of 217 

Contracting  work,  Advantages  and  disadvantages  of 233 

Contractor,  Duties  of 214 

Contracts,  Advertising 235 

' '        ,  Awarding 236 

Cost,  Relative,  of  sewers  of  different  capacities 41 

'    .     See  material  or  work  in  question. 

Cremation  of  sewage 6 

Cross-section  of  sewer,  Effect  of  shape  of,  upon  velocity 53,  65 

Cultivation  filter 474 

Curves,  Loss  of  head  in 56 

Cutting  sewer-pipe 293 

Dead-ends  in  sewers 103 

Defective  sewers,  Contractor's  responsibility  for 209,  211 

Delays  of  construction,  Provision  in  contract  for 211 

Deposits,  Sewage,  near  outlets 383 

Depth  of  sewage,  Minimum  permissible 61,  67 

'  *        sewer  desirable 1 16,  132 

' '  ' '    ,  Relation  of  Q,  S,  and  d  to 115 

Design,  Data  necessary  for  the 87,  90 

' '      ,  Principles  of  sewerage 95,  120 

Des  Moines,  Gauging  of  sewage  flow  at 25 

Diffusion  of  sewage  in  water 393 

Dilution,  Amount  of,  necessary  in  potable  water 386 

to  prevent  nuisance 363 

,  ,  required 388 

,  Disposal  by 359 

,  Conditions  affecting 363,  385,  386 

in  tidal  waters,  Requirements  for 5,  92,  98,  332 

' '      ,  Proportion  of,  necessary 392 

' '       ,  Purification  effected  by 389 

Discharge  into  rivers  and  tidal  waters.     See  Dilution. 

through  circular  sewers,  Effect  of  depth  upon 53 

' '       egg-shaped  sewers,  Effect  of  depth  upon 54 

"       sewers,  Table  of 48 

1 '       partly  full,  Calculating  the - 55 

Disinfecting,  Action  of  chlorine  in 472 

,  Cost  of 469,  47i 

,  Methods  of 467 

,  Results  from 468,  473 

Disk  for  cleaning  small  sewers  . ^ 


496  INDEX. 

PAGE 

Disposal,  Aims  of 361 

' '       ,  Commercial  aspect  of 362 

defined 359 

"       ,  Laws  affecting 12,  361,  363 

' '       ,  Principles  involved  in 362 

Distributors  for  trickling  niters 455 

Dortmund  tank 409 

Drainage  area,  Ascertaining  size  of 87,  90 

"  "  ,  Data  necessary  concerning 88 

districts 101 

* '        of  wet  soils 123,  313,  315 

Draining  Trenches.     See  Water,  Ground. 

Driving-cap  for  sheathing 281 

Dry-sewage  methods 2 

Dwelling,  Average  number  of  persons  in  a 19 

Earth-closet  system 5 

Egg-shaped  sewers,  Proportional  dimensions  of 67 

,  Advantages  of,  over  circular 67 

Electricity  for  treating  sewage,  Use  of 413,  414 

Electricity,  Formation  of  disinfectants  by 473 

Emscher  tank,  Description  of 423 

Engineer,  Power  of,  in  contract  work 214 

Engineer's  duties  before  construction 237 

* '  during  construction 250 

Estimate  of  cost,  Data  for  making 220 

Excavated  materials,  Classification  of 186 

*  *  ,  Placing  of,  on  streets 266 

Excavating  deep  trenches 267,  274 

"          machinery,  Advantages  of  using 187,  245,  271,  286,  334 

"  "        ,  Different  kinds  of 272,  274 

' '        ,  Economy  of 273 

* '          trenches  by  hand 266 

"  "     ,  Cost  of 224,213 

' c  "     ,  Specifications  for 186 

Excreta,  Amount  of,  per  capita 367,  373 

Extra  work,  Specifications  for 212 

Factories,  Amount  of  sewage  from 19 

Family,  Average  number  of  persons  in  a 19 

Field-book,  Form  of  notes  in 246,  255 

Filter,  Cultivation 474 

' '    ,  Definition  of 434 

* '      presses  for  sludge 481 

* '    ,  Theory  of  operation  of 434 

"    ,  Wave 474 

Filters,  Aeration  of 475 

'  *     ,  Mechanical 476 

"     ,  Thermal 476 


INDEX. 


497 


PAGE 

Filtration  beds,  Maintenance  of 443 

,  Cost  of 446 

' '        ,  Definition  of 436 

1 '       ,  Efficiency  of 441 

' '        ,  Methods  used  in 440 

* '        ,  Theory  of 432 

Final  estimate  book,  Method  of  keeping 253 

' '  ,  Definition  of 252 

,  Preparing 256 

' '    inspection 209,  256 

Fish,  Consumption  of  Sewage  by 395 

"    ,  Effect  of  sewage  upon 384,  385 

Flat-bottom  sewers 145 

Floats,  Use  of .* 92 

Flow  in  sewers,  Theory  of 44 

Flushing,  Appliances  for « 77,  166,  347 

' '         by  hand,  Methods  of 75,  348 

"  "  "         ,  Relative  cost  of  different 351 

' '       vs.  automatic  flushing 351 

' '         by  roof-water , 76 

' '       ,  Efficiency  of 74 

from  streams  and  tide-waters 76 

' '     water-mains  direct 79,  348 

'  *       ,  Intervals  between 70 

"       ,  Necessity  for 69,  8 1,  345 

1 1       ,  Proper  methods  of 72 

' '       ,  Sea-water  for 77 

' '       ,  Separate  sewers  without 74 

water,  Amount  of,  necessary 71 

Flush-tanks,  Amount  of  water  from 21,  78 

,  Automatic  apparatus  for 77,  166,  347 

,  Construction  of 165,  204,  306,  348 

,  Inspection  of 347 

,  Locating 129,  345 

,  Method  of  building 306 

,  Specifications  for 204 

,  Testing 257 

Foremen,  Number  and  character  of 262 

Foundations,  Forms  of 294,  307 

* '          ,  Materials  for 308 

,  Specifications  for 191 

,  where  needed 176 

Free  ammonia,  Definition  of 376 

Gangs,  labor,  Size  and  number  of 261,  263 

Gorged  sewers,  Relieving 137,  172 

Grade  cord,  Setting  and  using 241,  242 

' '      rod,  Form  and  use  of 244 


493  INDEX. 


PAGE 


Grade  stakes,  Use  of , 241,  246 

Grades  of  combined  sewers 60 

' '        house-sewers 59,  j  18 

' '        sewers,  Calculating u8 

11     ,  Desirable 118 

1 '     ,  Maximum 6r 

' '        storm-sewers 60,  1 18 

Gravel,  Specifications  for 185 

Grit  chamber,  Definition  of 406 

Ground-water.     See  Water,  Ground. 

Hose  for  cleaning  small  sewers 360,  324 

House-connections,  Capacity  of  four-inch 340 

,  Interference  of  storm-sewers  with 121 

,  Junction  of,  with  sewers 126 

,  Line  and  grade  of 126 

,  Locating 238,  247 

,  Method  of  cleaning 357 

,  Necessity  of  careful  construction  of 84,  125,  338 

,  Regulations  for 339,  344,  347 

,  Sewer-air  in 80 

,  Size  of 63,  340 

,  Ventilating  sewers  through 84,  342 

with  deep  sewers 175 

' '      sewage,  Amount  of 14,  97,  104 

' '     ,  Gaugings  of -. 21 

Hydraulic  radius,  Definition  of 45 

,  Formula  for,  in  circular  sewers 59 

' '  ,  Tables  of 53 

Hydrolytic  tank,  Description  of 425 

Imperfect  work,  Contractor  to  repair 211 

Imperviousness  of  ground  and  run-off 35,  108 

"  "         ,  Determining 108 

Incubator  test  .  .  . 378 

Injuries,  Responsibility  of  contractor  for 211 

Inlet  connections 127,  168 

,  Ventilating  sewers  through 84 

Inlets,  Construction  of 167,  306 

,  Locating 96,  1 29 

' '     ,  Specifications  for 204 

Inspecting  sewers 256 

Inspection-hole 340 

Inspection  of  house-drainage 344,  347 

' '  sewers,  Necessity  for 248,  345 

Inspector,  Duties  of 248,  251 

Intercepting-sewers 100,  137 

Interceptors 138 

"         ,  Leaping  weir 170 


INDEX.  499 

PAGB 

Interceptors,  Diverting 170 

Intersections  of  sewers 151,  209 

Invert  backing , 293,  300 

' '      blocks 147 

' '     ,  Definition  of * 241 

Inverted  siphons,  Construction  of 1 73 

1 '  ,  Principles  of  design  of 122,  1 72 

"  ,  where  used 65,  116,  247,  327 

Inverts  for  brick  sewers 150 

Iron  castings,  Specifications  for 182 

' '  ,  wrought,  Specifications  for 183 

Irrigation.     See  Broad  Irrigation. 

Joint-packing,  Specifications  for 185 

Joints,  Pipe-sewer 102,  154,  193,  317,  327 

"  ' '        ,  Concrete  around 291,  317 

' '    ,  Ward  flexible,  Cost  of  laying 332 

Kalamazoo,  Gaugings  of  sewage  flow  at 24 

Kuichling's  laws  of  run-off 32 

Kutter's  formula 46 

Laborers,  Housing  non-resident 276 

Lamp-holes,  Construction  of 165 

,  where  used 129,  247 

Laying  sewer-pipe,  Cost  of 224 

* '        ,  Specifications  for 197 

Leaks  in  sewers,  Stopping 197,  257,  317 

Legal  status  of  stream  pollution 364 

Leveling  necessary  for  designing 89,  91,  238 

Liernur  system  of  sewerage 7 

Lifting  sewage,  Methods  and  apparatus  for 133,  134 

* '     ,  when  necessary , 132 

' '      stations,  Location  of 136 

' '      ,  Number  of,  desirable 134 

Lines,  Locating  sewer 101,  240 

Manhole  bottoms 162,  304 

' l        buckets 165 

steps 158,  305 

tops 164,  245,  305 

' '        walls 164,  304 

Manholes,  Building,  in  quicksand 325 

"        ,  Cost  of 226 

1 1        ,  Crossing 160 

1  *        ,  Dimensions  of 158 

1 '        ,  Drop 160 

"        ,  Location  of 128,  157,  334 

"        ,  Materials  and  shapes  of 304 

"       ,  Method  of  building 304 

"          on  large  sewers 162 


500  INDEX. 

Manholes,  Purposes  of 84,  128 

,  Shallow I58,  306 

,  Specifications  for 203 

"        ,  Sub-drain 160,325 

Manufacturing  wastes  in  sewage ^68 

,  Removing,  from  sewage 4!4 

Map  required  for  designing 87,  91 

Masonry,  brick,  Specifications  for jg6 

sewers,  Materials  and  shapes  of 293 

,  stone  block,  Specifications  for !97 

stone,  Specifications  for T93 

work  in  winter 292,  306 

Masons,  Number  of,  required 263 

Materials  of  sewer  construction.     (See  also  material  or  appurtenances  in 

question.) i4Ij  I45 

Maul  for  driving  sheathing 281 

Measurement  of  work 214,  252 

Mechanical  filters 476 

Memphis,  Gaugings  of  sewage  flow  at 24 

Methylene  blue  test 378 

Mineralization,  Definition  of 429 

,  Methods  of  effecting 432 

Mirrors  for  inspecting  sewers 258 

Monthly  estimates,  Preparing 254 

Mortar,  Method  of  making 193,  296 

and  brick,  Handling 296 

n  in  Kutter's  formula,  Values  for 47 

Nitrates,  Definition  of 377 

Nitrification,  Definition  of 431 

'  *          .     See  Mineralization. 

Nitrites,  Definition  of 377 

Nitrogen  in  sewage,  Forms  taken  by 374,  377 

Notes  of  the  work 246,  251,  253,  254 

Nozzles  for  sprinkling  filters 460 

Nuisance,  Dilution  necessary  to  prevent 363 

Object  of  a  sewerage  system 13 

Obstructions,  Causes  of,  in  sewers 69 

' '         ,  Passing,  by  siphon 247 

Office  buildings,  Amount  of  sewage  from 19 

Old  sewers,  Using,  in  new  system 139 

Outlet,  Deer  Island,  Cost  of 331 

Outlets  for  sewerage  systems 89,  92,  117,  132,  137,  332 

' '     ,  Construction  of 331 

* '     ,  Reason  for  plurality  of 391 

Overflows 1 72 

Oxidation  of  sewage,  Desirability  of 429 

"  ,  Effect  of 376 


INDEX.  501 

PAGE 

Oysters,  Typhoid  fever  germs  in 385 

Packing,  joint,  Specifications  for  .  . 185 

Pail  for  earth-closet  or  pail  system 5 

' '    system 4 

Paving,  restoring,  Specifications  for 208 

Payments,  Times  of  making 217,  265 

Picks 269 

Piles,  Methods  of  driving 307 

Pills,  Use  of,  in  cleaning  sewers 260,  353 

Pipe,  broken,  Replacing,  in  sewers 339,  357 

' '   ,  cement,  Specifications  for 181 

1  i  ,      ' '        vs.  vitrified  clay 156 

' '   ,  drain,  Specifications  for 181 

"   ,     "    ,  Cost  of 223 

' l   ,  heavy,  Methods  of  laying  .  .  .  , 288 

' '   ,  House-drain 343 

' '   ,  iron,  Cost  of 223 

,  * '     layers,  Number  of,  required 263 

' '   ,  sewer,  Cutting 293 

",     "    ,Priceof 221 

"   ,     "    ,  Strength  of 153 

"   ,     "    ,  Thickness  of 152 

"     sewers,  Cleaning 260,  323,  353 

'  *     ,  Cost  of  laying 224 

"         "     ,  Imperfections  common  in 259 

"         "       in  quicksand 320 

'  *       in  wet  trenches 316,  323 

"     ,  Inspecting 250,  258 

' '     ,  Laying,  up  or  down  hill 287,  315 

* '         "-..,  Methods  of  laying 287,  317 

* '     ,  Specifications  for  laying 197 

' '   ,  two-foot  vs.  three-foot  lengths 156 

' '   ,  vitrified,  Specifications  for 1 79 

Pipes  and  conduits,  Interference  with,  by  contractor 188 

' '    ,  Water,  gas,  or  drain,  in  the  trench 270 

Plans,  sewerage,  Data  required  for 87 

Platforms  in  deep  trenches 267 

Plumbing,  Regulations  for  sanitary 339 

Pneumatic  systems 7 

Pollution  of  streams,  Effect  of 382 

' '  water,  ^tatutes  concerning 366 

Population,  Distribution  of,  in  families  and  dwellings 17 

* '        ,  Districts  based  on  density  of. 20,  100 

'  *         ,  Estimating  future  increase  in 19,  97 

' '  per  acre,  Rule  for  calculating 20 

Precipitation,  Chemicals  used  for 411,  413,  414 

"          ,  Cost  of 418 


502  INDEX. 

PAGE 

Precipitation ;  Effects  of  various  chemicals  in 411 

,  Methods  employed  in 416 

' '  tanks 417 

Private  property,  Sewers  on 104 

Privies a 

Profiles,  Information  to  be  shown  on 115,  121 

' '        necessary 89 

"      ,  Preparing 91,  115 

Providence,  Gaugings  of  sewage  flow  at 22 

Pumping,  hand,  Methods  of 309,  3 14 

* '       ,  steam,  Methods  of 310 

11       .     See  Lifting. 

Pumps,  Hand,  on  construction  work 309 

' '     ,  Steam,  on  construction  work 310 

'  *     ,  sewage,  Capacity  of,  necessary 133 

"     ,    "    ,  Kinds  of ,  in  use 135 

Purification  by  dilution 359 

1 1        ,  Chemical  changes  during 373 

' '        ,  Degree  of,  necessary 386 

' '        ,  where  required 364 

Quicksand,  Building  brick  sewers  in 245,  320 

,         ' '       manholes  in 325 

' '         ,          "       pipe  sewers  in 245,  320 

' '        ,  Detecting  presence  of 94 

' '         ,  Handling  trenches  in 264,  315,  318,  320 

* '        ,  Qualities  of 318 

1 1         ,  Removing,  from  pipe  sewers 323 

,  Sheathing  in 277,  279,  319 

R.     See  Hydraulic  radius. 

Raceways,  Method  of  crossing  under 335 

Railroad  crossings,  Construction  at 333 

"  ,  Specifications  for 188 

Railroads,  Sewers  near 334 

Rainfall,  Rates  of,  in  various  sections 29,  109 

Ransome  method  of  building  sewers  . .  1 303 

Relief  sewer,  Purposes  of f  1 72 

Removing  a  pipe  from  a  sewer 339 

Rivers,  Methods  of  crossing 326 

' '     ,  Discharging  sewage  into.     See  Dilution. 

'  *     ,  Sewage-pollution  of 363,  382 

Rock,  Determining  presence  of 93 

' '      excavation,  Cost  of 224 

' {  ' '        ,  Measuring 253 

"  "        ,Sewersin 176 

"  "        ,  Specifications  for 189 

Rods  for  cleaning  small  sewers 356 

Run-off  at  Nagpoor  reservoir f 35 


INDEX.  503 

PACiE 

Run-off  at  Washington,  D.  C 32 

' '     ,  Comparison  of  formulas  for 39 

4 '       conducted  through  gutters 43,  96 

* '     ,  Diagrams  for  calculating 31 

"     ,  Factors  of 28 

' '     ,  Formulas  for 36 

' '     ,  ' '  ,  Discussion  of 38 

* '     ,  Gaugings  of,  at  New  Orleans 31 

' '     ,  Kuichling's  laws  of 32 

' '     ,  Method  of  calculating 108 

"     ,  Roe's  table  for 38 

S,  Definition  of 45 

St.  Louis,  Gaugings  of  sewage  flow  at 24 

Sand,  Cost  of 227 

' l      for  mortar,  Specifications  for 183 

Sanitary  sewerage,  Requirements  of i 

Schenectady,  Gaugings  of  sewage  flow  at 23 

Screening,  Amount  removed  by : 403 

Screens,  Description  of 400 

Scum,  Septic  tank 420 

Sections  of  sewers 142 

Sedimentation,  Purification  by 390,  393 

,  Results  from 407 

tanks,  Construction  of 407 

"  "    ,  Designing 406 

Separate  system  vs.  combined 10 

"     defined . 9 

Septic  tank,  Construction  of 422 

,  Definition  of 419 

,  Function  of 422 

"  plants,  Cost  of 427 

Septic  tanks  and  settling  tanks,  Difference  between 419 

Sewage,  Causes  of  danger  from 3,  80,  326 

' l     ,  Composition  of 14,  367 

*      ,  Value  of 362 

Sewage.     See  House-  or  Storm-sewage. 

Sewerage,  Arguments  in  favor  of i,  2,  123,  232,  362 

Sewer-pipe.     See  Pipe,  Sewer. 

Shape  of  sewer  section 65,  142 

Sheathers,  Number  of,  necessary 262,  264 

Sheathing,  Driving-cap  and  maul  for 278,  281 

' '        ,  Horizontal 277,  281 

"        ,  Materials  and  dimensions  of 280,  282 

' '        ,  Removing 285 

"        ,  Skeleton 276,  282 

trenches,  Cost  of 224 

"  "       ,  Methods  of 276,283,319 


504  INDEX. 

PAGE 

Sheathing  trenches  on  steep  slopes 335 

"       ,  Specifications  for „ 188 

' '       ,  when  necessary 269,  275 

* '        ,  when  to  be  left  in 284 

Shone  Ejectors 7,  136 

Shoring  buildings 188,  286 

Shovels 269 

Sidewalks,  Sewers  under 102 

Silt-basins,  Use  and  construction  of 169 

Siphons,  Inverted.     See  Inverted  siphons. 

Sizes  of  house  sewers,  Method  of  determining 14,  59,  62,  104 

,  Minimum 63 

' '       sewers,  Calculating,  from  sewage  volume 104,  118 

' '       storm  sewers,  Method  of  determining 28,  59,  106 

,  Minimum 64 

Slate  beds,  Description  of 453 

Sludge,  Amount  of 483 

1 '     ,  Definition  of 416 

"     ,  Disposal  of 445,  478,  480,  482 

' '     ,  Filter  presses  for 481 

"     ,  Nature  of 478 

Specifications,  Classification  of 177 

,  Definition  of 177 

,  Requirements  of 1 78 

Splashing  disks  for  sprinkling  filters 463 

Sprinklers,  Comparing  efficiency  of 464 

Sprinkling  filter  nozzles 460 

' '     filters,  Construction  of 459 

* '  ,  Definition  of 456 

,  Rates  used  in 457 

* '  ,-  Results  obtained  by 458 

,  Theory  of  operation  of 456 

Staging  in  trenches,  Construction  of 267 

Steep  slopes,  Sheathing  trenches  on : 335 

Sterilizing  sewage 387,  413 

Stone,  masonry,  Specifications  for 182 

' '    ,  paving,  Specifications  for 182 

Stoneware  sewer-pipe.     See  Pipe,  Vitrified. 

Stores,  Amount  of  sewage  from 19 

Storm  overflows ' 138 

' '      sewage,  Data  for  determining  volume  of 106 

' '      sewerage,  Extent  of 96 

' '      sewer,  Determining  size  of 41,  50,  64,  1 18 

' '      water,  Amount  of,  to  be  provided  for 40,  42 

Storms,  Damage  done  by 41 

' '    ,  First-,  second-,  and  third-class 40 

Straining,  Importance  of 4°° 


INDEX.  505 

PAGE 

Street  surfaces,  Breaking,  for  trenches 266 

,  restoring,  Specifications  for 208 

Sub-drain  pipe,  Specifications  for 181 

Sub-drains,  Cleaning 323 

*  *         ,  Construction  of 1 74 

"          for  handling  ground-water 310,  315,  316 

in  quicksand 322,  323 

' '        ,  Inspecting 260 

* '        ,  Necessity  for 123 

"        ,  Outlets  for 124 

"        ,  Size  of 125 

4 '         ,  Specifications  for 202 

Sub-invert  spaces 176 

Surveys  necessary  for  designing 90 

System  of  sewerage,  Which,  to  adopt 12,  99,  133 

Tamping  trenches,  Cost  of 205 

,  Methods  of 206,  291,  293 

,  Specifications  for 206 

Tanks,  Precipitation 417 

' '     ,  Special  forms  of 477 

Templet  for  sewers 294 

* '      ,  Inspector's  or  skeleton 258 

Thermal  filters 476 

Tidal  reservoirs 132 

Timber,  Specifications  for 185 

Time-keeper,  Duties  of 262 

Toronto,  Gaugings  of  sewage  flow  at 23 

Trade  wastes,  Precipitating 414 

Traps,  Location  and  use  of 81,  169,  341 

Treatment  Sewage,  Aims  of 386 

' '      ,  Choice  of  method  of 484 

1  i     ,  Classification  of 397 

' '      ,  defined 359 

' '      ,  Method  of,  to  be  adopted 99 

' '      ,  methods,  General  discussion  of 398 

* '      ,  plants,  Cost  of 488 

"      ,      * '     ,  List  of  various 491 

"      ,      * c     ,  Structures  for 486 

Trench  machine.     See  Excavating  machine. 

Trench,  Storm-  and  house-sewer  in  the  same , 104 

Trenches,  Excavating 266 

1 '       ,  Giving  line  for 240,  266 

Trickling  filters,  Definition  of •. 456 

,  Distributors  for 455 

Tunnelling  trenches 268 

Typhoid-fever  from  polluted  water 384 

germs  in  oysters 385 


506  INDEX. 


PAGE 


Vegetable  organisms,  Absorption  of  sewage  by 395 

Velocity  in  sewers,  Effect  of  depth  upon 53 

1 '       ,  Formula  for 45 

11       ,  Table  of 48 

' '     ,  Maximum,  permissible 61 

"     ,  Minimum,  permissible  in  storm  and  combined  sewers 58,  60 

"     ,         "        ,  house-sewers 55,  59 

' '     ,  Uniform,  in  a  system 119 

Ventilation  of  sewers,  Methods  recommended  for 85,  342 

' '       ,  Necessity  for 79?  82 

"  "       ,  Various  expedients  for 82 

Vertical  tanks 409 

Vitrified  clay  pipe.     See  Pipe,  Vitrified. 

Walls,  Thickness  of  sewer 143,  151 

Water-carriage  system 7 

closet  tanks 342,  343 

' '      closets,  Location  of 343 

Water  consumption  and  sewage  flow 14 

"   .  "          ,  Estimating  future 16,  98 

in  various  cities 15 

' '     ,  ground,  Amount  of,  leaking  into  sewers 21,  155 

1 1     ,       ((      ,  Detecting  presence  of 94 

*'*-••,       "      ,  Driven  wells  for  lowering 316 

"     ,       '•<•-,  Handling 237,  308,  313,  316 

' '     ,       ' '      ,  Sub-drains  for  handling 310 

' '       in  trenches,  Specifications  governing 187 

' '     ,  Methods  of  constructing  sewers  under 327 

' '     ,  Tamping  trenches  with 208 

Wave  filter 474 

Weston,  W.  Va.,  Gaugings  of  sewage  flow  at 24 

Wet  and  quicksand  trenches,  Pipe-joints  in 317 

"  ' '  ,  Size  of  gangs  for 264 

11  /•*  .     See  Water,  Ground. 

Winter,  Masonry  work  in " 292,  306 

' '      ,  Pipe  laying  in 306 

Wooden-stave  pipe 142 

Working  gangs,  Size  and  number  of 262 


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